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Topical conference on Strangeness and Heavy-Flavour production in Heavy-Ion Collisions

The International Conference on Strangeness in Quark Matter (SQM 2017) will focus on new experimental and theoretical developments on the role of strange and heavy-flavour quarks in high energy heavy ion collisions and in astrophysical phenomena.

SQM 2017 will be the 17th edition of the conference series following the recent events in Berkeley (2016), Dubna (2015), Birmingham (2013) and Cracow (2011).

The scientific topics are

Strangeness and heavy quark production in nuclear collisions and hadronic interactions

Hadron resonances in the sQGP

Bulk matter phenomena associated with strange and heavy quarks

Strangeness in astrophysics

Open questions and new developments

Venue
The conference will take place in the Victor J. Koningsberger building that is located in the Science Park of Utrecht University. The venue is connected by frequent bus services to Utrecht city centre.

Conference Fee
The conference fee of 350€ (for participants who register and pay before 30 April 2017) and of 400€ (for those who register and pay after 30 April 2017) includes coffee breaks, lunches, the welcome reception, the excursion and the proceedings. All participants and accompanying persons are cordially invited to the conference dinner on Wednesday, 13 July 2017 (30€).

A graduate school on “The role of strangeness in heavy-ion physics” on 8-9 July 2017 will precede the conference. Students who apply and are selected for this school pay a reduced conference fee. Check this page for more information.

Koningsberger Building

Correlation femtoscopy allows one to measure the space-time characteristics of particle production in relativistic heavy-ion collisions due to the effects of quantum statistics and final state interactions. The main features of the femtoscopy measurements at top RHIC and LHC energies are considered as a manifestation of strong collective flow and well interpreted within hydrodynamic models employing equation of state with a crossover type transition between QGP and hadron gas phases. The femtoscopy at lower energies was intensively studied at AGS and SPS accelerators and is being studied now in the Beam Energy Scan program at the BNL Relativistic Heavy Ion Collider in the context of exploration of the QCD phase diagram. In this work the femtoscopic observables calculated for Au-Au collisions in a viscous hydro+cascade model vHLLE+UrQMD and their dependence on the EoS of thermalized matter are presented. Some possible opportunities to perform such studies with respect to the NICA energies are also discussed.

Different aspects of chiral phenomena are considered on the basis of comparison of generalized thermodynamic distribution function and quantum-field calculation of one-loop triangle diagram. The consequences for particle polarization in heavy ion collisions are discussed.

Study of clusters and hypernuclei formation within PHQMD+FRIGA model at the NICA energies20m

We report on the results on the dynamical modelling of cluster formation with the new combined PHQMD+FRIGA model at Nuclotron and NICA energies. The FRIGA clusterisation algorithm, which can be applied to the transport models, is based on the simulated annealing technique to obtain the most bound configuration of fragments and nucleons. The PHQMD+FRIGA model is able to predict isotope yields as well as hyper-nucleus production. Based on present predictions of the combined model we study the possibility to detect such clusters and hypernuclei in the BM@N and MPD/⁠NICA detectors.

Heavy quarks (charm and beauty) are unique probes used to understand the properties of the QCD medium produced in ultra-relativistic heavy-ion collisions. Due to their large masses, they are created in the early stages of the collisions and experience the full evolution of Quark-Gluon Plasma (QGP). They interact with its consitutents and lose energy as they travel through the medium. Heavy quarks can be studied by measuring electrons coming from the semi-leptonic decays of heavy-flavour hadrons.

Two-particle angular correlation measurements are a powerful tool to study jet quenching especially in ${p}_{\rm{T}}$ regions where direct jet identification is difficult. In such measurements, we observe a near-side peak around $\Delta\varphi \approx 0$, formed by particles associated to a high-${p}_{\rm{T}}$ trigger particle, and an away-side peak around $\Delta\varphi \approx \pi$, formed by back-to-back dijets. By studying heavy-flavour angular correlations triggered by electrons from heavy-flavour hadron decays, we can access information about heavy-flavour jet quenching in the QGP. Near-side correlations can be studied to understand if the fragmentation and hadronization of heavy-quarks are modified by medium effects.

In this poster, we present the current status of the ALICE measurement of azimuthal angular correlations of high-${p}_{\rm{T}}$ heavy-flavour decay electrons with charged particles in Pb-Pb collisions at $\sqrt{{s}_{\rm{NN}}} = 5.02$ TeV from the LHC Run 2. The measurements from Pb-Pb collsions will be compared to p-Pb collisions at $\sqrt{{s}_{\rm{NN}}} = 5.02$ TeV.

$K^{*}(892)^{\pm}$ and $\phi$(1020) production in pp collisions at $\sqrt{s}$ = 5.02 TeV with ALICE at the LHC20m

In this work we report the first results on $K^{*}(892)^{\pm}$ and $\phi$(1020) production in pp collisions at $\sqrt{s}$ = 5.02 TeV with the ALICE detector. The hidden strangeness $\phi$-meson is reconstructed at mid-rapidity via its hadronic decay channel $\phi \rightarrow$ K$^{+}$K$^{-}$, by employing different techniques, without and with kaon identification using the information from the Time Projection Chamber and Time of Flight detectors. The $K^{*\pm}$ is reconstructed via a two-steps decay process where the resonance undergoes a strong decay to K$^{0}_{S}$ + $\pi^{\pm}$ and then the K$^{0}_{S}$ decays weakly to $\pi^{+}$ + $\pi^{-}$. Measurements of these resonances in pp collisions at $\sqrt{s}$ = 5.02 TeV constitute a reference for the measurements in Pb-Pb collisions at the same center-of-mass energy and contribute to the study of energy and multiplicity dependence of particle production in pp collisions. Results presented here include the transverse momentum ($\it p_{T}$) spectra, integrated yields and $\langle p_{T} \rangle$ for $K^{*\pm}$ and ${ \phi}$. These are compared with results from other LHC energies and with the predictions from QCD-inspired event generators.

A study of the strange vector meson spin alignment with the AMPT model20m

Observables sensitive to the vorticity allow us to study the fundamental property of the hot and dense nuclear matter created in high-energy nuclear collisions.
Global polarization parameters of identified particles can be extracted from the
azimuthal distribution of particles with respect to the event plane. The spin alignment of vector meson such as $\phi$ meson and $K^{\star}$ could be sensitive to the vorticity of the colliding system and its space-time evolution. In this presentation, we will present results from a multi-phase transport (AMPT) model that is modified to include the spin alignment information of $\phi$ and
$K^{\star}$ mesons. We will discuss the extraction of spin alignment parameters from event plane reconstruction, and study how hadron interactions could
influence the spin alignment observables based on final state particles.

Two-particle correlations in azimuth and pseudorapidity are used to explore the properties of the hot and dense medium created in heavy ion collisions by studying collective effects and jet quenching. The study of correlations in small systems (pp and p-Pb collisions) is relevant as a baseline for Pb-Pb collisions and to understand jet properties, as well as possible cold nuclear matter effects in the presence of the nucleus and collective behaviour in small systems. A double-ridge structure has been observed in these small systems for light-flavor particles, but the physical meaning of this structure is still in debate, in particular regarding the role of hydrodynamics and initial conditions in such systems. Extending these measurements to the heavy-flavour sector is therefore crucial to improve the current understanding of the small systems.

Heavy quarks (charm and beauty) are dominantly produced in the initial hard scatterings of the collision due to their large masses. In case a medium is formed they experience its full evolution. In this work the heavy quarks are studied by measuring electrons coming from the semi-leptonic decays of hadrons that contain a heavy quark.

In this poster, we will present current status of the angular correlations of heavy-flavour hadron decay electrons with charged particles in p-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV in the ALICE central barrel acceptance ($|\eta| < 0.8$) using the Run 2 dataset. This dataset offers increased statistics when compared to Run 1 allowing us to improve the performance of this measurement.

Measurements of azimuthal correlations can be used to probe the anisotropy of produced particles, and are therefore sensitive probes of the initial conditions of the collision.
Moreover, the measurement of anisotropy in p-Pb collisions may provide additional insights into the possible collectivity
in this small system originally motivated by the measurements of multi-particle azimuthal correlations.
In this contribution, we present the recent results on the azimuthal anisotropy coefficients $v_{n}$
of identified hadrons, namely $\mathrm{\pi, K, p}$, and also the $\mathrm{K^{0}_{S}}$ meson and $\Lambda$ baryon which carry strangeness, in p-Pb collisions at $\sqrt{s_\mathrm{NN}} = 5.02$ TeV recorded with the ALICE experiment at the LHC.
The phenomena of mass ordering and number of constituent quark scaling will be addressed.
In addition, the comparison of the experimental measurements to various model calculations will be discussed.

Estimation of transport coefficients in an anisotropic QGP using a quasiparticle approach20m

We investigate the shear viscosity ($\eta$) and electrical conductivity ($\sigma_{\rm{el}}$)
of the anisotropic quark-gluon plasma (QGP) medium.
Relativistic Boltzmann kinetic equation has been solved
in the relaxation time approximation to calculate the shear viscosity and electrical conductivity. We use the quasiparticle model to estimate these transport coefficients and discuss the connection between them. We compare the bag model result with the quasiparticle model which give the possible hint to the role of thermal mass in the electrical conductivity of QCD plasma.
We compare our results with the corresponding results obtained in different model as well as lattice calculations for both at zero and finite chemical potential.

First results of $\rm{K^{*}(892)^{\pm}}$ production in pp collisions at $\sqrt{s} = \rm{13} \hspace{0.15 cm} \rm{TeV}$ with ALICE at LHC20m

The study of hadronic resonances plays an important role both in elementary and in heavy-ion collisions as it can provide information about strangeness production and the hadronic phase of the system. Since the lifetimes of short-lived resonances are comparable with the lifetime of the fireball formed in heavy-ion collisions, regeneration and rescattering effects can modify the measured yield especially at low transverse momentum. The ratio of the resonances to that of longer lived particles can therefore be used to estimate the time interval between the chemical and kinetic freeze-out. Measurements in pp collisions constitute a baseline for studies in heavy-ion collisions, they can provide information for tuning QCD-inspired event generators and contribute to the understanding of particle production mechanisms. In particular, the resonance $\rm{K^{*}(892)^{\pm}}$ is important because of its very short lifetime ($\sim $4 fm/$c$).

In this contribution, we will report the first results at LHC energies for $\rm{K^{*}(892)^{\pm}}$ resonance in pp collisions at $\sqrt{s}$ = 13 TeV. $\rm{K^{*}(892)^{\pm}}$ has been measured at mid-rapidity via its hadronic decay channel $\rm{K^{*}(892)^{\pm}}\rightarrow \rm{K^{0}_{\rm{S}}}+ \pi^{\pm}$, with the ALICE detector. In particular, the transverse momentum ($p_{\mathrm{T}}$) spectrum compared with model predictions, integrated yields and $\langle p_{\mathrm{T}}\rangle$ will be presented.

The study of the J/$\psi$ production in pp collisions provides important information on perturbative and non-perturbative quantum chromodynamics. The production of the heavy-quark pair can be described perturbatively while its hadronisation into quarkonium state is a non-perturbative process. These processes are not fully understood and additional experimental data are necessary to further constrain the theoretical production models. In this work we report studies of J/$\psi$ production in pp collisions at a centre-of-mass energy of $\sqrt{s}$ = 13 TeV at mid-rapidity with ALICE. The J/$\psi$ are reconstructed via their dielectron decay channel in events where at least one of the decay electrons was triggered on by the Electromagnetic Calorimeter (EMCal). The availability of a high-$p_{\rm T}$ electron trigger enhances the sampled luminosity significantly relative to the available minimum-bias triggered data set and extends the $p_{\rm T}$ reach for the J/$\psi$ measurement.
Additionally, the usage of EMCal for particle identification at high $p_{\rm T}$ ranges provides a very good electron/hadron separation. Using these data, the J/$\psi$ measurement is performed in the transverse momentum interval $5 < p_{\rm T} < 20~\textrm{GeV}/c$.

K*(892)0 Production in pp Collisions with ALICE Detector at the LHC20m

The lifetimes of short-lived hadronic resonances are comparable to the one of the hadronic phase of the medium produced in high-energy collisions. Thus, these resonances are sensitive to the re-scattering and regeneration processes in the time interval between the chemical and kinetic freeze-out, which might affect the resonance yields. The measurements in pp collisions are used as a reference for nuclear collisions and provide in addition information for the tuning of event generators inspired by Quantum Chromodynamics (QCD). In this contribution, we present recent results on $K^*(892)^{0}$ obtained by the ALICE experiment in pp collisions at several collision energies and event multiplicities. Results on transverse momentum spectra, yields and their ratio to long-lived particles will be presented and the energy and multiplicity dependence will be discussed. The measurements will be compared with model predictions and measurements at lower energies.

Latest Results with HIJING++ for Strange Quark Matter from RHIC to LHC Energies20m

In the high-energy heavy-ion physics community the FORTRAN based HIJING Heavy Ion Jet Interaction Generator code is commonly used, originally developed by Xin-Nian Wang and Miklos Gyulassy [1]. Although it was intended to describe the heavy-ion collisions occurring at RHIC energies, it has still many applications with todays higher collision energies. However, the technological advancement nowadays makes it clear that the upgrade of the code is getting more and more important.

The new, C++ based and soon-to-be-published HIJING++ that we introduce will be the successor of the original HIJING[2]. It will be a state-of-the art Monte Carlo code with all of the capabilities of the original event generator and much more. It is designed to be future-proof in the sense of computer hardware and software as well. In this study we present the current state of the development and give an outlook of the forthcoming features.

We present our latest result on strange quark matter including heavy quark production as well.

[1] Wang, X-N.; Gyulassy, M. HIJING 1.0: A Monte Carlo Program for Parton and Particle Production in High Energy Hadronic and Nuclear Collisions. Comput.Phys.Commun.1994, 83(307).

Measurement of $\rm{D}^{*+}$-meson production in p--Pb and pp collisions with ALICE at the LHC20m

Measurements of open heavy-flavour production in p--Pb collisions at the Large Hadron Collider (LHC) allow the study of cold-nuclear matter effects, such as shadowing, $k_T$ broadening and initial-state energy loss. Heavy quarks (charm and beauty) are a valuable probe for the Quark-Gluon Plasma created in Pb--Pb collisions, since they are produced in hard scattering processes in the initial stages of the collision.
The comparison between p--Pb and Pb--Pb collisions makes it possible to distinguish between cold- and hot-nuclear matter effects, the latter expected to be present in high-energy Pb--Pb collisions.
Besides providing a reference for p--Pb and Pb--Pb collisions, the measurement of the $\rm{D}^{*+}$ $p_T$-differential production cross section in pp collisions also provides an excellent test of next-to-leading-order perturbative QCD calculations in hadronic collisions at the TeV energy regime.
In ALICE, $\rm{D}^{*+}$ mesons are reconstructed at mid-rapidity via the hadronic decay channel $\rm{D}^{*+}\to\rm{D}^0\pi^+\to \rm{K}^-\pi^+\pi^+$. Cold-nuclear matter effects on the $\rm{D}^{*+}$-meson yield in p--Pb collisions are studied via comparison to the binary scaled $\rm{D}^{*+}$-meson yield in pp collisions. This comparison is quantified by means of the nuclear modification factor $R_{\rm{pA}}$.

In this contribution, we present the latest measurement of $\rm{D}^{*+}$-meson production in pp collisions at $\sqrt{s}= 7$ and 8 TeV from Run I and in pp collisions at 13 TeV and p--Pb collisions at $\sqrt{s_{\rm{NN}}}= 5.02$ TeV from Run II.

Measurement of electrons from heavy-flavour hadron decays in pp collisions at √s = 13 TeV in the ALICE experiment20m

Proton-proton collisions at the LHC are an excellent source of experimental data that allow us to test particle-production processes calculable with perturbative QCD. Heavy quarks (charm and beauty) are an interesting probe because, due to their large masses, the energy scales involved in their production are large. Therefore their production cross section can be calculated with perturbative QCD. In addition to that, the pp data provide a necessary reference for the study of the Quark-Gluon Plasma (QGP) produced in Pb-Pb collisions. Since heavy quarks are produced in the very beginning of the collision and survive all the QGP evolution, the comparison between the pT spectra of electrons from heavy-flavour hadron decays in Pb-Pb and pp collisions can provide information on how the heavy quarks loose energy by interacting with the QGP constituents. In the poster, we will show the status of the measurement of electrons from heavy-flavour hadron decays in pp collisions at √s = 13 TeV. The data were collected in the run 2 of LHC with the ALICE experiment. Electron identification is performed with the Time Projection Chamber and Time-Of-Flight detectors, up to 4 GeV/c. All analysis steps necessary for measuring the heavy-flavour electron spectra will be discussed, including the data-driven method used to subtract the large photonic background component at low transverse momentum.

Speaker:
MrsCamila de Conti

17:40

Measurement of strange and multi-strange hadron production in high-multiplicity pp collisions at 13 TeV with ALICE20m

Measurements of identified particle production as a function of the event multiplicity in proton-proton (pp) and proton-nucleus collisions have recently gained interest for the investigation of particle production mechanisms in small systems and how they relate to those in the larger system created in nucleus-nucleus collisions.
In particular, recent results reported by the ALICE Collaboration show a progressive increase of the hyperon-to-pion ratios as a function of charged particle multiplicity at mid-rapidity from pp up to Pb-Pb collisions.
In this work, we present new results on strange and multi-strange hadron production as a function of multiplicity, based on the analysis of a large sample of high-multiplicity triggered events in pp collisions at $\sqrt{s}=$ 13 TeV collected by ALICE in 2016.
These measurements extend the previous reach in multiplicity obtained from the analysis of the minimum bias sample, allowing for a wider overlap with the multiplicity range spanned with p-Pb collisions as well as approaching multiplicities present in peripheral Pb-Pb collisions.
Transverse momentum spectra and integrated yields are presented and compared with previous measurements for different collision systems and energies.

Multiplicity dependence of pion, kaon and proton production in pp collisions at $\sqrt{s}$ = 7 and 13 TeV20m

Measurements of particle production in high-multiplicity pp collisions are crucial for the understanding of the collective-like features observed in small systems and reminiscent of those present in heavy-ion collisions. The ALICE detector, with its excellent tracking and particle identification capabilities, provides unique possibilities for the systematic study of light-flavour hadrons at the LHC. In this work we report on the minimum bias and multiplicity-dependent production of pions, kaons and protons in pp collisions at 7 and 13 TeV. Results include transverse momentum ($\rm p_{\rm T}$) spectra, average $\rm p_{\rm T}$ and yield ratios. These measurements serve as a necessary baseline for the study of the multiplicity-dependent enhancement of multi-strange particle production in small systems.

Аnisotropic flow presents a unique insight into heavy ion collision physics. The presented poster reveals the prospects of studying elliptic flow at the NICA/MPD facility through the UrQMD model.
Presented are results on elliptic flow for simulated and reconstructed hadrons at the planned NICA energy range.

Study of flow, fluctuation and CME background in Isobaric collisions using a transport model.20m

Knowing the initial geometry and fluctuations in heavy-ion collisions has recently been shown to have important consequences on interpreting the data from the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC) experiments. It is also believed that measurement of higher order flow coefficients and their fluctuations can substantially improve the constraints on
the transport properties of the system formed in high energy heavy-ion collisions. In recent years, the experimental search for the Chiral Magnetic Effects (CME) has been intensively performed in heavy-ion collisions at the RHIC and the LHC. To detect the CME, a three-point correlator, $\gamma_{\alpha\beta} = \langle \cos(\phi_{\alpha} + \phi_{\beta} - 2\Psi_{RP}) \rangle $ was proposed, where $\phi$ is the azimuthal angle of a charged particle, the subscript $\alpha(\beta)$ denotes the charge sign of the particle (positive or negative), $\Psi_{RP}$ is
the angle of the reaction plane of a given event, and $\langle ...\rangle$ denotes an average over all particle pairs and all the events. It has been recently shown in simplistic Monte-Carlo (MC) simulations that isobaric collisions will provide a better handle to constrain initial spatial anisotropy to similar magintude while allowing the magnetic field to vary considerably. With this overview, RHIC has now proposed to carry out an isobaric ($_{40}Zr^{96}+ _{40}Zr^{96}$, $_{44}Ru^{96}+ _{44}Ru^{96}$) heavy-ion collisions program at $\sqrt{s_{NN}}$ = 200 GeV. Due to the lack of partonic and hadronic interactions, the existing MC simulations of isobaric collisions are unable to predict the amount of flow, fluctuations and the CME background due to $v_{2}$. Therefore, it will be convincing to understand and estimate these observables with models which incorporates collectivity and able to reasonably reproduce experimental measurements.
This work presents final momentum space observables from isobaric
($_{40}Zr^{96}+ _{40}Zr^{96}$, $_{44}Ru^{96}+ _{44}Ru^{96}$) collisions generated using a transport (AMPT) model with default settings for RHIC energies. Two difference scenarios with different amount of deformation in $_{44}Ru^{96}$ and $ _{40}Zr^{96}$ nuclei has been studied. In this presentation, the evolution of initial spatial anisotropies and its fluctuations will be presented as a function of centrality ($N_{part}$). The final monentum space anisotropy $v_{n}$ ($n$=2, 3, 4) would be presented as a function of centrality. The as well as a function of transverse momentum $(p_{T})$ for different centrality classes. The results from these isobaric collisions are compared with Au+Au collisions in AMPT as well as with the results from experiments. The evolution of the magnetic field as a function of centrality and the background for the CME ($\langle \cos(\phi_{\alpha} + \phi_{\beta} - 2\Psi_{RP}) \rangle$) will be presented and compared with measurements from data.

Study of non-extensive parameters in transverse momentum spectra of hadrons20m

Since firstly proposed by C. Tsallis, the q-non-extensive statistics has been of great interest both experimentally and theoretically. One of the most important applications is the non-extensive effects on the transverse momentum (pT) spectra of both strange and non-strange particles in heavy-ion collisions, where it shows a power-law tail for the large pT range.

To clarify not only the experimental data but the non-extensive statistics itself, we investigate the latest pT spectra of various identified charged hadrons within different centralities in p+Pb collisions. With respect to the mass dependence and strangeness dependence as well, the corresponding fitting parameters are well analysed.

In this presentation we aim at understanding the non-extensive parameter q and the temperature T from fitting the different pT spectra using the Tsallis-Pareto formula. And the relations between them will be also demonstrated.

Studying the effects of multi-parton interactions on typical heavy-ion observables20m

Recent measurements performed in high-multiplicity proton-proton (pp) and proton-lead (p-Pb) collisions have shown features that are reminiscent of those observed in lead-lead (Pb-Pb) collisions.
The origin of these features is, however, still controversial, with collectivity, initial state effects and multipartonic correlations all possibly contributing.
The pp measurements have in the past been successfully modeled by mechanisms such as multi-parton interactions and color reconnection. We now have an opportunity to investigate if these effects can mimic collectivity in a high multiplicity regime.

In this work, we use the PYTHIA event generator to investigate how typical heavy-ion observables are affected in a scenario in which a large number of partonic interactions took place. Observables related to the event shape and identified particle production, including strange particles and resonances, are studied. Finally, we also discuss the prospect of how to best perform experimental event selection in pp and p-Pb collisions and still preserve the expected physics from multi-parton interactions as opposed to introducing any potential selection biases.

Bottomonium are produced in the heavy ion collisions and their production is modified compared with elementary collisions. This modification in the production of bottomonia happens due to the presence of hot and dense QCD matter, named as quark-gluon plasma (QGP) formed in ultra relativistic heavy ion collisions. We
present here a comprehensive model based on color screening, collisional damping due to exchange of soft gluons between the $b\bar{b}$ pair and gluonic dissociation caused by absorption of gluon which led $b\bar{b}$ pair transition
from color singlet to color octet state. We have also taken cold nuclear matter effect, mainly shadowing effect, in our consideration as it modifies the quarkonia production in heavy ion collisions. We employ the above model to analyze the data on Upsilon suppression measured in terms of nuclear modification factor, $R_{AA}$ as the function of centrality and transverse momentum, $p_{T}$. Finally, we compare our results with the $\Upsilon$(1S) data obtained from Pb+Pb collisions at $\sqrt{s_{NN}}= 2.76$ TeV at LHC energy. We find that our model describes the LHC data reasonably well.

The results from HI collisions at RHIC and LHC indicate that the quark-gluon state formed is a strongly interacting one. Hagedorn had suggested that a strongly interacting system can be equivalently described as a system of non-interacting entities with corresponding masses. Given the above, we seek “particle/mass states”, which could equivalently describe the equation of state of QCD matter.
Taking as input lattice calculations for (2+1) flavours, as well as for SU(3) gauge field, we develop an effective description of the lattice QCD pressure and specific entropy at zero baryon-chemical potential. We use two parameters: the number of states 'gt' and the average particle mass. The description is carried out for the inclusive 3-flavour system, as well as the gauge field sector and the quark sector.
The calculated parameters of the total and the quark systems have as their low temperature limit the corresponding parameters of the Hadron Resonance Gas (HRG). The number of states for all sectors (total, gluon and quark) converge, above T ≈ 230 MeV, close to the number of states of an ideal quark-gluon phase, indicating the existence of colour states at these conditions. The corresponding high average masses, however, suggest that the entities are strongly interacting.
The number of states 'gt' and the average mass of the system containing only quarks are found to decrease steeply with increasing temperature between T ≈ 150 and 160 MeV, an interval contained within the region of the chiral transition. The quality of the fit (value of χ2) can be used as a tool to locate regions of best effective descriptions in terms of the parameters 'gt' and average mass, as well as points of transition between them.

Speaker:
Apostolos Panagiotou
(National and Kapodistrian University of Athens (GR))

COSMOS

Koningsberger

Data-driven analysis of the temperature and momentum dependence of the heavy quark transport coefficients20m

Heavy quarks have been considered valuable probes of the quark-gluon plasma (QGP). It has been found that heavy quarks propagating through a hot and dense QGP lose energy and develop flow. The interacting strength between the heavy quarks and medium ($\hat{q}/D_s$), although not directly measurable, can be estimated by comparison of model calculations with experimental observables. Currently, most of the models are able to quantitatively either reproduce the experimental measurements of heavy quark energy loss $R_{\mathrm{AA}}$ or the collective behavior $v_2$. However, they still face significant challenges for simultaneously describing both together.

Commonly, an extraction of the heavy quark transport coefficient relies on manually varying the parameters of the calculation until satisfactory agreement with experimental data is obtained. Here, we propose a systematic and quantitative approach to the data-driven analysis of the heavy quark diffusion coefficient using Bayesian statistics. We apply the Bayesian analysis to an updated full space-time evolution model for heavy quarks: including a parameterized initial condition model TRENTO, an in-medium improved Langevin transport model, a hybrid hadronization model with both, fragmentation and recombination, and UrQMD for hadronic final state interactions. Note the evolution of the QGP medium is already calibrated by a state-of-the-art Bayesian analysis performed on an event-by-event hydrodynamical model VISH(2+1) with shear and bulk viscous corrections.

We demonstrate the feasibility of describing experimental data at both RHIC and LHC energies using a generalized parameterization for the temperature and momentum dependence of the heavy quark diffusion coefficients. The likelihoods of the parameters, which indicate their functional form, are obtained in an unbiased manner. We can thus quantify the most probable parameter values as well as the uncertainties and correlations among them, and obtain for the first time a proper estimation of the heavy quark transport coefficients from experimental data.

We present a new derivation of the heavy quark diffusion coefficient in a strongly-coupled plasma using the AdS/CFT correspondence. Our main result is that, unlike some previous calculations, our diffusion coefficient does not increase with heavy quark velocity: we find that the effect of momentum fluctuations smoothly interpolates between light and heavy flavors. Taking our diffusion coefficient derivation as fundamental, we use the fluctuation-dissipation theorem to predict a strong-coupling heavy quark drag that is slightly different from the original calculations of Gubser and Herzog et al. We then show recent numerical work that supports some of the key assumptions in our analytic derivation. Incorporating our novel heavy flavor drag and diffusion into an energy loss model, we compare with pQCD predictions of Nahrgang et al. at the partonic level, and with data from LHC for heavy flavor observables. While our predictions are in good agreement with the data from LHC, the partonic momentum correlations exhibit an order of magnitude difference in low momentum correlations to the pQCD calculations. We thus propose heavy flavor momentum correlations as a distinguishing observable of weakly- and strongly-coupled energy loss mechanisms.

Correlation between heavy flavour production and multiplicity in pp collisions at high energy in the multi-pomeron exchange model20m

The multiplicity dependence of heavy flavour production in pp-collisions at LHC energies is studied in the framework of the multi-pomeron exchange model [1-3].
The model is based on the introducing the string collectivity effects in pp collisions, which modifies the bulk multiplicity and transverse momenta, leading to non-trivial pt-n correlation. The string collectivity strength parameter is fixed by experimental data on multiplicity and transverse momentum correlation in a wide energy range (from ISR to LHC). The particles discrimination is implemented according to Schwinger mechanism [4], allowing to qualitatively describe the strangeness production and its correlation with multiplicity [5].

For the heavy flavour production, we assumed that its yield is proportional to the number of initial pomeron exchanges, whereas the total charged particle multiplicity is influenced by the string collectivity. We demonstrate, that the faster-than-linear growth of the open and hidden charm production, observed in experiment [6], can be related to the reduction of the total multiplicity due to string overlapping and interaction.
The extension of the approach for p-A collisions is also discussed.

The research was supported by the grant of the Russian Science Foundation (project 16-12-10176).

Heavy-flavor observables are excellent probes of the properties of the in-medium interactions, the medium properties and the degrees of freedom of the quark-gluon plasma created in heavy-ion collisions. Progressing toward a quantitative description, we describe, in EPOSHQ, the dynamics of heavy quark coupled systematically to the EPOS3 model: heavy-quarks are produced from the EPOS3 flux tube initial conditions both in momentum and in coordinate space and subsequently propagated in parallel to the fluid dynamical evolution of the viscous QGP. Hadronization of the heavy quarks via coalescence and fragmentation and particlization of the fluid enable us to investigate the importance of the final hadronic rescatterings on the heavy-flavor observables.

This global description allows us to draw conclusions from the comparison to a variety of heavy-quark observables in different systems and constrain important aspects in our underlying model for the in-medium interaction, such as the contributions stemming from elastic and inelastic energy loss, or the mass dependence by comparing charm and bottom quark dynamics. In this contribution we address the question of the event by event (EBE) correlation betweeen flow harmonics of heavy and light mesons. At low transverse momentum, we find a good correlation of average flows but unexpectedly large fluctuations of EBE $v_2$ and $v_3$ for heavy flavors, which cannot be explained by the usual scheme relying on underlying common bulk flow. We then investigate whether such fluctuations could originate from initial state effect regarding heavy quark distribution, offering possible new perspectives on the thermalization of heavy quarks in the quark gluon plasma.

BBG 165

In hydrodynamic approach to heavy ion collisions, hadrons with nonzero spin produced out of the fluid can acquire polarization via spin-vorticity thermodynamic coupling mechanism [1]. The hydrodynamical quantity steering the polarization is the thermal vorticity, that is minus the antisymmetric part of the gradient of four-temperature field $\beta^\mu=u^\mu/T$.

Based on this idea, it has been shown in the framework of cascade+viscous hydro model, UrQMD+vHLLE [2] that in Au-Au collisions at RHIC Beam Energy Scan (BES) the mean polarization of Lambda hyperons grows with decreasing collision energy up to 1.5% at $\sqrt{s_{NN}}=7.7$ GeV RHIC Au-Au collisions. This goes in line with recent measurements of Lambda polarization by STAR experiment [3].

We complement the existing Lambda polarization studies at RHIC BES [2] by exploring:

polarization splitting between Lambda and anti-Lambda, and related effect of magnetic field at hadronization

centrality dependence and connection between angular momentum of the system and polarization of produced Lambda

rapidity and transverse momentum dependence of the polarization

We also explore the longitudinal component of polarization, which is dominant for nonzero $p_T$ at top RHIC and LHC energies.

Correlation measurements, such as the anisotropic flow, constrain the kinematic ($\eta/s$) and bulk ($\zeta/s$) viscosity of the quark-gluon plasma created in heavy-ion collisions, and give insight into the hadronization mechanisms. Particle production mechanisms can also be studied via other correlation techniques that can statistically separate the hadron production associated with a high-$p_{\rm T}$ trigger particle (jet) from that of the bulk, in order to investigate the baryon-to-meson anomaly at intermediate $p_{\rm T}$ observed in central heavy-ion collisions.

In this talk we present the elliptic ($v_2$) and higher harmonic ($v_3$, $v_4$) flow coefficients of $\pi^\pm$, $K^\pm$, $p(\bar{p})$ and the $\phi$-meson for a wide range of $p_{\rm T}$, measured in Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV with the ALICE detector. These measurements allow for a unique testing of the presence of mass ordering at low $p_{\rm T}$, and baryon and meson scaling at intermediate $p_{\rm T}$. We also present the $\Lambda/K^{0}_{s}$ ratio in the bulk and jet peak regions, measured for $2 < p_{\rm T} < 8$ GeV/$c$ using 2.76 TeV Pb-Pb data, where the results suggest that the enhancement of baryons compared to mesons arises from the soft, collective part of the medium (the bulk), and not from the hard processes (modified jet fragmentation).

Event-by-event elliptic flow harmonic distributions $p(v_{2})$ are measured in PbPb collisions at $\sqrt{s_{NN}} = 5.02$~TeV using the CMS detector for the integrated $p_{T}$ range $0.3 < p_{T} < 3.0$~GeV/$c$ and pseudorapidity range $\left| eta \right|<1.0$. In order to gain insight on the nature of the initial geometry fluctuations, cumulant flow harmonics are calculated from the moments of the $v_2$ probability distribution $p(v_{2})$. A fine-level splitting between the higher-order cumulants is observed. The skewness with respect to the reaction plane is estimated from the cumulants and found to be negative, which suggests a non-Gaussian nature for the initial-state fluctuations, as predicted by hydrodynamic models. These observations suggest a non-Gaussian nature of the initial-state fluctuations. Furthermore, assuming that the flow harmonics are linearly proportional to the initial-state eccentricities, the $p(v_{2})$ distributions are fitted using an elliptic power law parameterization to study the initial-state geometry fluctuations.

Collective flow of open heavy flavour in heavy ion collisions at the LHC energies with CMS20m

The measurement of heavy flavour production and collective flow is a powerful tool to study the properties of the high-density QCD medium created in heavy-ion collisions as heavy quarks are sensitive to the transport properties of the medium and may interact with the QCD matter differently from light quarks. In particular, the comparison between the nuclear modification factors (RAA) of light- and heavy-flavour particles provides insights into the expected flavour dependence of in-medium parton energy loss. Furthermore, azimuthal anisotropy coefficient (vn) of heavy-flavor particles provide insights into the degree of the thermalization of the bulk medium at low pT, and unique information about the path length dependence of heavy quark energy loss at high pT. Using the large statistics heavy ion data samples collected during the 2015 and 2016 LHC runs, high precision open charm and beauty measurements are performed with the CMS detector in a wide transverse momentum range. This allows us to set an important milestone in our understanding of the interactions between heavy quarks and the medium. In this talk, the most recent results of v2 and v3 of D0 mesons in PbPb collisions at 5.02 TeV are presented and compared to the same results for charged hadrons at the same energy. Latest results on nuclear modification factor of D and B mesons in pPb and PbPb collisions are also presented.

BBG 161

One of the most exciting and puzzling observations in ultrarelativistic
p+A reactions is the fairly large harmonic flow (such as v2(pT) and
v3(pT) coefficients). On one hand, the flow seems to be consistent with
hydrodynamic simulations [1], suggesting a high degree of thermalization
even in such very small collision systems. On the other hand, several
non-thermal mechanisms can also generate azimuthal correlations. For
example, there are inherent angular correlations in multi-gluon
production in QCD [2]. Anisotropic escape from the collision zone is yet
another non-thermal mechanism that results in flow anisotropy [3].

Intrinsic space-momentum correlations in quantum mechanics also lead to
significant harmonic flow [4]. Unlike hydrodynamic evolution, where
momentum anisotropies need time to be generated by pressure gradients,
the quantum anisotropies are inherent at the initial condition to
hydrodynamics. (Such correlations, therefore, are also very different
from pre-flow generated during thermalization.) They arise because of
the Heisenberg uncertainty relation that prohibits perfect simultaneous
localization in both momentum and coordinate space. This kind of
anisotropy, therefore, has two main features: it gets more pronounced
the smaller the system size, but it vanishes in the infinite temperature
("classical") limit.

Up to now these quantum anisotropies have only been calculated for
nonrelativistic particles, which is unfortunate because the results lose
their validity for transverse momenta exceeding the particle mass (pT >~
m), right where anisotropies start to become really significant and
interesting [4]. I will present new results from a calculation for
relativistic particles, and show that intrinsic quantum anisotropies are
indeed significant at pT ~ 1-2 GeV. I will also discuss how the
intrinsic anisotropies are affected by the subsequent expansion dynamics
of the system.

First measurement of $\Sigma^{0}$-production in proton induced reactions on a nuclear target at E$_{kin}$ = 3.5 GeV*20m

The measurement of $\Sigma$ hyperons is rather difficult because of their abundant decay into neutral particles.
For this reason, data are available only for few energy points in pp, pA and AA collisions, in particular, the energy gap between 2 and 4 GeV
remains unexplored. Also, since $\Sigma$ hypernuclei have not been measured so far, nothing is known quantitatively from experiments
about the $\Sigma$-N interaction. For these reasons precise measurements of $\Sigma$ hyperons are needed in the field of hadron physics.
We have studied the production of neutral $\Sigma^{0}$ baryons in the nuclear reaction p + Nb at an incident proton
energy $E_{kin}$ = 3.5 GeV. The measurement has been performed with the HADES experiment setup at GSI, Darmstadt.
From 4.2$\times$ 10$^{9}$ recorded events, $\Sigma^{0} \rightarrow \Lambda^{0} \gamma$ decays were identified via the
decay $\Lambda^{0} \rightarrow p \pi^{-}$ coincident with $e^{+}e^{-}$ pairs from external gamma conversion.
Experimental details, analysis procedures and background determination are presented. The momentum and the rapidity distribution
of the particle and an observed total of about 220 candidate events is used to pin down the $\Lambda$/$\Sigma$ ratio.
The obtained numbers and spectra are compared to predictions from transport model calculations and are discussed in the
context of thermal particle production in nuclear fireballs.
*supp. by BMBF(05P15WOFCA), GSI F$\&$E(5802045) and the Excellence Cluster Universe

Quarkonium production in pp and p-A collisions with ALICE at the LHC20m

Quarkonia are mesons formed of either a charm and anti-charm quark pair ($\rm{J}/\psi$, $\psi(2S)$), or a beauty and anti-beauty quark pair ($\Upsilon$(1S), (2S) and (3S)). In high-energy hadronic collisions such as those delivered by the LHC between 2010 and 2016, quarkonium production results from the hard scattering of two gluons in a process which occurs very early in the collision followed by the hadronization of the heavy quark pair in a bound state. In pp collisions, quarkonium measurements help characterize production mechanisms and provide a reference baseline for p-A and A-A measurements. In p-A collisions these measurements quantify cold nuclear properties such as nuclear shadowing, gluon saturation, energy loss or break-up of the c\bar{c} pair in the medium. Disentangling cold nuclear effects from hot nuclear properties of the Quark-Gluon Plasma (QGP)is essential for the evaluation of the size of hot matter effects on charmonia in a QGP environment.

While charmonia are produced rather abundantly in such collisions, interpreting the measurement of their inclusive production is complicated by the presence of a sizable non-prompt contribution from the decay of b-hadrons. Bottomonia on the other hand have much smaller production cross sections but no non-prompt contribution. Moreover, their heavier mass makes them more suitable for perturbative QCD calculations.

In this presentation we will report on forward rapidity ($2.5 < y < 4$) $\rm{J}/\psi$ and $\psi(2S)$ production measured in pp collisions at center of mass energies $\sqrt{s}=5.02$ and $13$~TeV, using data collected at the LHC in 2015. Together with similar measurements performed at $\sqrt{s}=2.76$, $7$ and $8$ TeV, these results constitute a stringent test for models of charmonium production. In particular, they will be compared to NRQCD and FONLL calculations, which describe prompt and non-prompt charmonium production, respectively.

First Run-2 results on the J/$\psi$ and $\psi$(2S) production measurements in p-Pb collisions at sqrt{s_{\rm{NN}}}= 8.16 TeV, at forward and backward rapidities, will also be presented, together with new mid-rapidity J\psi results at sqrt{s_{\rm{NN}}}= 5.02 TeV. The J/$\psi$ and $\psi$(2S) nuclear modification factors will be compared to Run-1 results as well as theoretical calculations and will be interpreted in terms of cold nuclear matter effects.

$J/\psi$ production as a function of event multiplicity in pp and p-Pb collisions with ALICE20m

The availability at the LHC of the largest collision energy in pp collisions allows a significant advance in the measurement of $J/\psi$ production as function of event multiplicity. The interesting relative increase observed with data at the LHC at $\sqrt{s} = 7$ TeV and at RHIC at $\sqrt{s} = 200$ GeV is studied now at unprecedented multiplicities for pp collisions. The newest measurement performed at mid-rapidity in pp collisions at $\sqrt{s} = 13$ TeV in the dielectron decay channel, facilitated by triggering on high-multiplicity events, allows the comparison to $J/\psi$ production in p-Pb collisions at similar multiplicities.

We will compare our newest measurements on the $J/\psi$ yields as a function of event multiplicity in pp collisions at $\sqrt{s} = 13$ and 5.02 TeV to those obtained in p-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV at mid- and forward rapidity and at $\sqrt{s_{\rm NN}} = 8.16$ TeV at forward rapidity. The results are also discussed in comparison to predictions from available theoretical models and to data at lower energies.

BBG 169

Parallel session strangeness

Convener:
Domenico Elia
(INFN Bari)

09:00

Processes of hypernuclei formation in relativistic ion collisions20m

The study of hypernuclei in relativistic ion collisions open new
opportunities for nuclear and particle physics. The main processes
leading to the production of hypernuclei in these reactions are
(1) the disintegration of large excited hyper-residues (target-
and projectile-like), and (2) the coalescence of hyperons with other
baryons into light clusters. We use the transport, coalescence and
statistical models to describe the whole process, and demonstrate
the advantages over the traditional hypernuclear methods: A broad
distribution of predicted hypernuclei in masses and isospin
allows for investigating properties of exotic hypernuclei, as well
as the hypermatter both at high and low temperatures.
We point at the abundant production of multi-strange nuclei and new
bound/unbound hypernuclear states. The realistic estimates of
hypernuclei yields in various collisions are presented [1].
Other processes well known in normal reactions: evaporation,
fission, multifragmentation break-up are calculated in the case of
hypermatter [2]. There is a saturation of the hypernuclei production
at high energies [1], therefore, the optimal way to pursue this
experimental research is to use the accelerator facilities of
intermediate energies, like FAIR (Darmstadt) and NICA (Dubna).

The production and properties of $K^+$, $K^-$ and $\phi$ in cold nuclear matter generated in pion-nucleus reactions ($\pi^- + A$, $A = C, W$) at $p_{\pi^-}= 1.7$~GeV/c has been investigated with the HADES setup at SIS18/GSI.
Of particular interest is the $K^-$ absorption in nuclear matter which should be driven by strangeness exchange processes on one ($K^- N\rightarrow Y\pi$) or more nucleons ($K^- NN\rightarrow YN\pi$). On the contrary, $K^+$ does not undergo strong absorption processes and can be treated as quasi particle within nuclear matter, providing stringent constraints on the production mechanism of strange hadrons. In this context, also the $\phi$ production and absorption ($\phi\rightarrow K^+K^-$, $BR \sim 48.9\%$) off light and heavy nuclear targets is studied.
In this talk, we are presenting evidence of the $K^-$ absorption on the basis of the $K^-/K^+$ ratios in both nuclear environments (C, W) and the obtained cross-section inside the HADES acceptance. In addition, the $\phi$ absorption in a nuclear medium is discussed by comparing the production off carbon and tungsten as well as the $K^-$ production in terms of the $\phi$ feed-down.
* supported by the DFG cluster of excellence "Origin and Structure
of the Universe" and SFB 1258

Particle production and azimuthal anisotropy of strange hadrons in U+U collisions at STAR20m

The primary goal of relativistic heavy-ion collisions is to seek and characterize a new state of nuclear matter, called the quark-gluon plasma (QGP), where quarks and gluons are deconfined due to the high temperature and energy density achieved in such collisions. Measurements of invariant yield of strange hadrons can provide information about the particle production mechanism and transport coefficients for the system formed in heavy-ion collisions. The higher order flow coefficients can help in constraining the initial conditions of hydrodynamic simulations for a precise extraction of transport properties.

U+U collisions are believed to produce higher energy density and number of particles than what is achievable in collisions of spherical nuclei like Au+Au or Pb+Pb at the same incident energy. For a given impact parameter of collision the initial eccentricity are different for Au+Au and different configuration of U+U collisions. Therefore, In addition to higher energy density and number of particles, U+U collisions can be use to constrain initial conditions in heavy-ion collisions. In this work, we will present transverse momentum ($p_{T}$) spectra of $K_s^0$, $\Lambda$($\bar{\Lambda}$), $\Xi$($\bar{\Xi}$) and $\Omega(\bar{\Omega})$ in U+U collisions at $\sqrt{s_{NN}} =$ 193 GeV in the STAR experiment at RHIC. We will also present centrality and transverse momentum dependence of flow coefficients $v_{n}$ ($n$ = $2,3,4$) of strange hadrons ($K_s^0$, $\Lambda$ and $\phi$) at mid-rapidity ($|\eta| < 1.0$). The mass dependence of these $v_{n}$ coefficients will be shown. A systematic comparison of the results with Au+Au collisions at $\sqrt{s_{NN}} =$ 200 GeV will be presented.

The measurement of $\phi$ mesons provides a unique and complimentary method for exploring properties of the hot and dense medium created in the relativistic heavy ion collisions. It has a relatively small hadronic interaction cross section and is sensitive to the increase of strangeness (strangeness enhancement), a phenomenon associated with soft particles in bulk matter. Measurements in the dilepton channels are especially interesting since leptons interact only electromagnetically, thus carrying the information from their production phase directly to the detector. Measurements in different nucleus-nucleus collisions allow us to perform a systematic study of the nuclear medium effects on $\phi$ meson production. The PHENIX detector provides the capabilities to measure the $\phi$ production in a wide range of transverse momentum and rapidity to study these effects. In this talk, we present measurements of the $\phi$ mesons in a variety of collision systems at $\sqrt{s_{NN}}$ = 200 GeV. In case of small systems, the data are compared with AMPT calculations to study the various cold nuclear medium effects involved in $\phi$ meson production.

Coffee corner, Koningsberger building

10:50
→
12:30

Parallel BES: 1BBG 165 ()

BBG 165

Parallel session BES

Convener:
Alexandre Suaide
(IFUSP)

10:50

Kaon femtoscopy in Au+Au collisions from the Beam Energy Scan at the STAR experiment20m

Quantum Chromodynamics calculations predict that under sufficiently high temperature or energy density nuclear matter undergoes a phase transition from hadrons to a state of deconfined quarks and gluons, the Quark-Gluon Plasma. The properties of this novel state of matter have been extensively studied in high-energy nuclear collisions at RHIC.

Two-particle correlations at small relative momenta reveal the space-time characteristics of the system at the moment of particle emission. The femtoscopic analyses of kaons can serve as a cleaner probe of the studied system than measurements with pions as they are less affected by resonance decays. Since kaons contain strange quarks and have smaller cross-section with hadronic matter, measurements with kaons can be sensitive to different effect and/or earlier collision stages.

In this talk, I will present the STAR preliminary results on femtoscopic correlations of like-sign kaons from Au+Au collisions at Beam Energy Scan energies. The measured kaon source radii are studied as a function of collision energy as well as centrality and transverse pair mass $m_\mathrm{T}$. In addition, high-statistics dataset of Au+Au collisions at $\sqrt{s_\mathrm{NN}}$=200 GeV allows more detailed and precise study including extraction of freeze-out parameters using Blast-Wave parameters.

Moreover, I will present results from measurements of the system of unlike-sign kaons which contains $\phi$(1020) resonance. In the region of the resonance, the correlations due to the strong final-state interaction exhibit high sensitivity to the space-time extents as it was theoretically predicted. The measured unlike-sign kaon correlation function from 200 GeV Au+Au collisions are compared with Lednický's model including the final-state interaction as well as the resonance within the femtoscopic framework.

Anisotropic flow ($v_n$) measurements can provide important constraints for initial state models and for precision extraction of the temperature dependence of the specific shear viscosity $\eta/s$. Recent STAR measurements for rapidity even dipolar flow $v^{even}_1$ confirm the important influence of momentum conservation, as well as the characteristic dependencies on $\sqrt{s_{NN}}$ , centrality and $p_T$, expected when initial-state geometric fluctuations act in concert with hydrodynamic-like expansion to generate $v^{even}_1$. Dipolar flow measurements will be presented and discussed for a broad range of transverse momenta, $p_T$, and centrality intervals for Au+Au Beam Energy Scan ($\sqrt{s_{NN}}~=~ 7.7~-~200$ GeV), $U+U$ ($\sqrt{s_{NN}}~=~193~GeV$), and Cu+Au, Cu+Cu, d+Au and p+Au ($\sqrt{s_{NN}}~=~200~GeV$) collisions.

The recent BES data of the energy dependent $κσ^2$ for net protons in Au+Au collisions presented large deviations from the statistical baselines at lower collision energies, and non-monotonic behavior at around 20 GeV, which indicates possible signals for the existence of the QCD critical point [1].

In our recent paper [2], we introduce a freeze-out scheme to the dynamical models near the QCD critical point. Our model calculations for the static critical fluctuations on the freeze-out surface shows that the $C_4$ and $κσ^2$ data of net protons can be roughly described. However, $C_2$ and $C_3$ are always over-predicted due to the positive static critical fluctuations. After solving the time evolution equations of the various cumulants of the sigma field, the BNL group found the Skewness and Kurtosis could change their sign after the evolution, which indicates that dynamical critical fluctuations could solve the sign problem of $C_3$ [3]. However, such BNL approach cannot be easily combined with our freeze-out scheme to compared with the experimental data since only the zero mode of sigma field are considered there, which already erase the needed spatial information.

Within the framework of Langevin dynamics, we simulate the dynamical evolution of the fluctuating sigma field in position space and calculate the cumulants of the sigma field in the critical regime[4]. Our numerical simulations show that $C_2$ automatically increases as the system evolves in the critical regime, which represents the spontaneous increase of the chiral field’s correlation. Besides, for both $C_3$ and $C_4$, the sign in the earlier times can be remembered during the dynamical evolution due to the memory effects near the critical point[4]. Combined with the freeze-out scheme developed in [2], our calculation provides a possible way to qualitatively describe the different cumulants data of net protons in experiments.

Fluid dynamical fluctuations drive a system constantly out of equilibrium in connection with dissipative properties such as shear and bulk viscosity. The interaction of the fluctuations leads to a renormalization in the equation of state and in the transport coefficients. These effects are particularly important near phase transitions and in small systems. In an era of the high-precision extraction of QGP transport properties, it is crucial to incorporate the contributions from fluctuations into our models. Moreover, the critical fluctuations in the diffusive net-baryon density, which are searched for in the beam energy scan (BES) programs at RHIC and SPS as experimental signal for the conjectured QCD critical point, develop dynamically from fluid dynamical fluctuations.

In this talk, we discuss the effect of fluid dynamical fluctuations that are consistently propagated. For LHC physics, we focus on fluctuations in the energy-momentum tensor. The nonlinearities in fluid dynamics lead to cutoff-dependent corrections in the equation of state which we quantify for static systems. Moreover, we analyze correlation functions and the time-evolution of fluctuations in the thermodynamic quantities. For BES physics, we study the dynamics and nonlinearities of critical phenomena related to fluctuations in the net-baryon density. We show under which conditions Gaussian and non-Gaussian cumulants emerge from purely white noise. The influence of finite-size and finite-resolution effects as well as exact baryon number conservation are discussed. Performing real-time fluid dynamical simulations, we observe the formation of critical phenomena in the fluctuations of the net-baryon density - a crucial step toward a realistic modeling of critical point signals in heavy-ion collisions.

Supervised learning with a deep convolutional neural network is used to identify the QCD equation of state (EoS) employed in relativistic hydrodynamic simulations of heavy-ion collisions. The final-state particle spectra \rho(p_T,\Phi) provide directly accessible information from experiments. High-level correlations of \rho(p_T,\Phi) learned by the neural network act as an "EoS-meter", effective in detecting the nature of the QCD transition. The EoS-meter is model independent and insensitive to other simulation input, especially the initial conditions. Thus it provides a formidable direct-connection of heavy-ion collision observable with the bulk properties of QCD.

COSMOS

Parallel session heavy flavour

Convener:
Steffen A. Bass
(Duke University)

10:50

Overview of Heavy-Flavored Jets at CMS20m

The energy loss of jets in heavy-ion collisions is expected to depend on the mass and flavor of the initiating parton. Thus, measurements of jet quenching with identified partons place powerful constraints on the thermodynamic and transport properties of the hot and dense medium. Furthermore, recent results that constrain the jet production mechanism will shed additional light on the contributions of leading and next-to-leading order heavy flavor jet production with regard to the global energy loss picture. To this end, we present recent results measuring spectra and nuclear modification factors of jets associated to charm and bottom quarks in both pPb and PbPb collisions, as well as measurements of dijet asymmetry of pairs of b-jets in PbPb collisions.

Measurements of charm hadron production and anisotropic flow in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV with the STAR experiment at RHIC20m

Heavy flavor quarks, owing to their large masses, are predominantly produced through initial hard scatterings in heavy-ion collisions and thus are ideal probes to study the properties of the strongly coupled Quark Gluon Plasma (sQGP) also produced in these collisions. For example, study of the heavy flavor anisotropic flow can help understand the nature of the interactions between heavy quarks and the medium as well as the bulk properties of the medium. In particular, the first order anisotropy (directed flow), $v_{1}$, can provide information about heavy quark dynamics at early times. It is also predicted that the magnetic field present in the early stages of the collisions can induce large $v_{1}$ for heavy flavor mesons and can therefore be used to study such magnetic field.

Measurements of charm hadron spectra can provide further information on charm quark interactions and hadronization in the QGP. The modifications to charmed hadron spectra in heavy-ion collisions ($R_{AA}$) are sensitive to the energy loss of charm quarks, which in turn depends on the interactions between charm quarks and the medium. On the other hand, if the coalescence mechanism, observed for light flavor hadrons, also plays a significant role for charm quark hadronization in the QGP, enhancements in the yield ratios of $\mathrm{D_s^{\pm}}$ and $\mathrm{\Lambda_c}$ to non-strange charmed mesons can be expected.

We use the STAR Heavy Flavor Tracker (HFT) to reconstruct the heavy flavor hadrons, via their hadronic decay channels, in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV. The first measurement of the directed flow of $D^{0}$ and $\overline{D^{0}}$ mesons is presented as a function of particle rapidity, and compared to that of light hadrons. Measurements of the elliptic ($v_2$) and triangular flow ($v_3$) of $D^{0}+\overline{D^{0}}$ mesons will also be presented and compared to model calculations. We also show measurements of $R_{AA}$ for $\mathrm{D^{0}}$ and $\mathrm{D^{\pm}}$ mesons as well as the yield ratios of $\mathrm{D_s^{\pm}/D^0}$ and $\mathrm{\Lambda_c/D^0}$. The implications of these results on the understanding of the charm quark dynamics and the degree of charm quark thermalization in the sQGP medium, will be discussed.

Measurement of D-meson nuclear modification factor and elliptic flow in Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV with ALICE at the LHC20m

Open heavy-flavour mesons are a unique tool to study and characterize the properties of the Quark-Gluon Plasma (QGP), formed in heavy-ion collisions at high energy. Given their large masses, heavy quarks are produced in the initial stages of the heavy-ion collisions, and therefore they experience the whole system evolution, loosing energy interacting with the medium constituents. Thus, the measurement of the nuclear modification factor ($R_{\rm AA}$) of open heavy flavours can provide important information about the colour-charge and parton-mass dependence of the energy loss. In addition, the measurement of the elliptic flow ($v_2$) at low $p_{\rm T}$ can give insight into the participation of the heavy quarks in the collective expansion of the system and their thermalization in the medium. Moreover, the study of the $v_2$ at high $p_{\rm T}$ allows us to investigate the path-length dependence of parton energy loss. These two observables can also help us to understand possible modifications of heavy-quark hadronization in the medium. In particular, the role of the recombination mechanism can be studied via the comparison between D mesons with and without strange-quark content.

In this talk, the latest results on the production of D$^0$, D$^+$, D$^{*+}$ and D$^+_{\rm s}$ mesons at central rapidity measured via the exclusive reconstruction of their hadronic decays in Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV with ALICE will be presented. In particular, the $p_{\rm T}$-differential $R_{\rm AA}$ and $v_2$ of D mesons measured for different centrality classes will be shown and compared to predictions from theoretical models. Finally, the Event-Shape Engineering (ESE) technique applied to the D-meson elliptic flow in semi-central Pb-Pb events will be also presented, to investigate the influence of initial geometry fluctuations to heavy-flavour production.

Measurement of heavy-flavour production, correlations and jets with ALICE in Pb-Pb collisions with ALICE20m

Heavy-flavour (charm and beauty) production provides relevant information to understand the strongly interacting medium, Quark-Gluon-Plasma (QGP), formed in heavy-ion collisions at ultra-relativistic energies. Heavy quarks are produced primarily in the initial hard partonic interactions, and they propagate through the QGP. A strong suppression of heavy-flavour hadron production has been observed in the most central heavy-ion collisions with respect to binary-scaled pp collisions at intermediate and high $p_{\rm{T}}$. This is ascribed to energy loss of heavy flavours in the dense matter. In addition, the positive $v_{2}$ (elliptic flow) observed at low $p_{\rm{T}}$ in semi-central heavy-ion collisions suggests that heavy flavours participate in the collective motion of the system. These results indicate strong interaction of heavy quarks in the medium.

Further understanding of properties of heavy quarks in the QGP can be obtained by measurements of jets and azimuthal correlation of particles originating from heavy flavours, and which are sensitive to the possible modification of fragmentation of heavy quarks. Such measurements in pp and p-Pb collisions allow studies of jet properties, and address to investigate cold nuclear matter and collective effects of heavy quarks.

In this presentation, recent ALICE measurements of the $R_{\rm{AA}}$ and $v_{2}$ of leptons, electrons at mid-rapidity ($|y|

Charmonium production in pPb and PbPb collisions at 5.02 TeV with CMS20m

Charmonium states, such as the J/$\psi$ and $\psi$(2S) mesons, are excellent probes of the deconfined state of matter, the Quark-Gluon Plasma (QGP). The understanding of charmonia production in PbPb collisions requires the inclusion of many phenomena, such as dissociation in the QGP and statistical recombination, on top of cold nuclear matter effects (modifications of nPDFs, initial-state energy loss, nuclear break-up). Measurements of charmonia production in pPb collisions are crucial in order to disentangle the QGP-related effects from cold nuclear matter effects. In this talk, final results on the relative J/$\psi$ and $\psi$(2S) modification, based on the pp and PbPb data collected at \mbox{$\sqrt{s_{\mathrm{NN}}}$} $= 5.02$ TeV by CMS in 2015, will be reported. In addition, new prompt and nonprompt J/$\psi$ results in PbPb collisions at the same center-of-mass energy, including the nuclear modification factor $R_{AA}$, will be presented over a wide kinematic and centrality range ($3

Two-particle correlations as a function of $\Delta\eta$ and $\Delta\varphi$ are used in all collision systems to study a wide range of physical phenomena. Examples include the collective behaviour of the QGP medium, jets, quantum statistics or Coulomb effects, conservation laws, and resonance decays.

In this talk, we report measurements of the correlations of identified particles and their antiparticles (for pions, kaons, protons, and lambdas) at low transverse momenta in pp collisions at $\sqrt{s} = 7$ TeV, recently submitted for publication by the ALICE Collaboration [arXiv:1612.08975]. The analysis of identified particles in pp collisions reveals differences in particle production between baryons and mesons, which reflect the specific conservation laws for these quantum numbers. The correlation functions for mesons exhibit the expected peak dominated by effects of mini-jet fragmentation and are reproduced well by general purpose Monte Carlo generators. For baryon pairs where both particles have the same baryon number, a near-side anti-correlation structure is observed instead of a peak. Such effects have usually been connected to conservation laws in $e^{+}e^{-}$ collisions and were thought to be under theoretical control; however, our results present a challenge to the contemporary models (PYTHIA, PHOJET). This effect is further interpreted in the context of baryon production mechanisms in the fragmentation process.

Energy and multiplicity dependence of strange and non-strange particle production in pp collisions at the LHC with ALICE20m

The study of energy and multiplicity dependence of hadron production in proton-proton (pp) collisions provides a powerful tool to understand similarities and differences between small and large colliding systems. In this talk we present new mid-rapidity measurements of the $p_\mathrm{T}$ distributions and yields of unidentified charged hadrons as well as of pions, kaons, protons, K$^{0}_{\rm S}$, $\Lambda$, $\Xi$ and $\Omega$ in pp collisions at $\sqrt{s}$ = 5.02, 7 and 13 TeV.

The comparison of results at $\sqrt{s}$ = 13 TeV to earlier results at 7 TeV provides insights about the energy dependence of the strangeness enhancement. The multiplicity dependence is studied using various multiplicity estimators, in the forward and central rapidity regions, to understand possible selection biases. The production at high $p_\mathrm{T}$ of strange mesons and baryons, as well as of inclusive charged particles, is compared to other hard processes, such as D-meson and J/$\psi$ production. Comparisons between data and expectations from commonly-used Monte Carlo event generators will be presented. The extension of some of these measurements to very high multiplicity events (comparable to multiplicity in peripheral Pb-Pb collisions) will be also discussed.

Azimuthal anisotropies such as the elliptic flow $v_2$ are important tools for the study of the properties of the quark-gluon plasma (QGP). Recent studies with parton transport models suggest [1,2] that most parton $v_2$ comes from the anisotropic escape of partons, not from the hydrodynamic flow, even for semi-central Au+Au collisions at $\sqrt {s_{NN}}=200$ GeV. In this talk we will study the flavor dependence of the parton escape mechanism and address whether the escape mechanism is also dominant for heavier quarks such as strange and charm quarks [3,4]. We use a multi-phase transport (AMPT) model, which can reasonably describe the experimental data for the bulk matter [5]. We follow the entire evolution history of quarks of different flavors in AMPT and focus on the developments of strange and charm $v_2$ in heavy ion as well as small system collisions at RHIC and LHC energies. By performing the azimuth-randomized tests, we extract the relative contributions of the escape mechanism to the $v_2$ of light, strange, and charm quarks. In contrast to naive expectations, we find the charm $v_2$ to be much more sensitive to the hydrodynamic flow than lighter quark’s $v_2$. Our finding thus indicates that heavy quark flow may be better probes of the QGP properties than light quark flow.

Particle production and collectivity in high-multiplicity pp and pPb collisions at the LHC with CMS20m

Studies of particle yields and azimuthal correlations for inclusive and identified charged particles are presented in small collision systems of pp and pPb at the LHC with the CMS detector. Charged pions, kaons, and protons are identified via their energy loss in the CMS silicon tracker. The pT spectra and integrated yields are studied as a function of multiplicity and center-of-mass energies. In high-multiplicity events, a long-range near-side correlation, known as the "ridge", has been observed, similar to that in AA collisions that is often attributed to a fluid-like QGP. CMS studied this correlation in detail by extracting the anisotropy Fourier coefficients, v_n, for different particle species, and also via two- and multi-particle correlations. Latest results in pp at 13 TeV and pPb at 8.16 TeV are presented this talk, which provide important insights to the nature of the ridge in small collision systems.

BBG 169

Parallel session strangeness

Convener:
Dieter Roehrich
(University of Bergen (NO))

10:50

J/psi production in proton-lead collisions at 8 TeV with the LHCb detector20m

We present new results on J/psi production in p-Pb collisions, using the data collected in 2016 by LHCb at 8 TeV nucleon-nucleon center-of-mass energy. The LHCb experiment has the unique property to study heavy-ion interactions in the forward region (pseudorapidity between 2 and 5) with a fully instrumented detector. Both forward and backward rapidities are covered thanks to the possibility of beam reversal. Cold Nuclear Matter (CNM) effects are probed through measurements of nuclear modification factors and forward-backward production of both prompt and displaced J/psi. With respect to the results based on the 5 TeV sample collected in
2013, an increase in luminosity by a factor 20, other than the larger charm production cross-section, allow a remarkable improvement of the experimental accuracy. Results are compared with theoretical predictions modeling different CNM effects.

Strange and heavy hadrons production from coalescence plus fragmentation in AA collisions at RHIC and LHC20m

We study the $\Lambda_c/D$ ratio and $p/\phi$ at RHIC and LHC within a realistic implementation of coalescence model.
The evolution of the partonic stage is described by the relativistic Boltzmann equation tuned at a fixed shear-viscosity to entropy-density ratio $\eta/s$ and a realistic equation of state.
Such an approach recovers the universal features of the ideal hydrodynamics.
In a coalescence plus independent fragmentation approach we calculate the $p_T$ spectra and anisotropic flows $v_n$ of the main hadrons:
$\pi, K, p, \bar{p},\Lambda, D, \Lambda_c, \phi$ in a wide range of transverse momentum. Our approach correctly describes the
baryon-to-meson ratios $p/\pi,\bar{p}/\pi, \Lambda/K$ that reach a value of the order of unit at $p_T \sim 3 GeV$.
In particular we show that in a coalescence plus fragmentation approach one predicts a nearly $p_T$ independent $p/\phi$ ratio up to $p_T \sim 4 GeV$ followed by a significant decrease at higher $p_T$ . Such a behavior is
driven by a similar radial flow effect at $p_T < 2 GeV$ and the dominance of fragmentation for $\phi$ at larger $p_T$.
Moreover in the same framework we evaluate the $\Lambda_c/D$ ratio at RHIC and LHC finding a substantial enhancement with respect to $pp$ collisions.

$\phi$ meson production at forward rapidity in pp and Pb-Pb collisions with ALICE at the LHC20m

Quantum Chromodynamics predicts the occurrence of a phase transition from the hadronic matter to a plasma of deconfined quarks and gluons (Quark-Gluon Plasma) at extreme conditions of temperature and energy density. Ultrarelativistic heavy-ion collisions provide the means to study this phase of matter in the laboratory.

Strangeness production is a key tool to understand the properties of the medium formed in heavy-ion collisions: an enhanced production of strange particles was early proposed as one of the signatures of the QGP. The $\phi$ meson, due to its $s \bar s$ valence quark content, provides insight into strangeness production.

The ALICE experiment has measured $\phi$ meson production in the dimuon channel at the forward rapidity ($2.5 < y < 4$) in pp and Pb-Pb collisions at several center of mass energies.

Results in pp collisions at center of mass energies $\sqrt{s} = 5.02$, $8$ and $13$ TeV will be reported. They will complement the previously published results at $\sqrt{s} = 2.76$ and $\sqrt{s} = 7$ TeV, providing a solid baseline for Pb-Pb collisions. In Pb-Pb, the preliminary $\phi$ meson $p_\mathrm{T}$ spectra for different centrality classes and the yield as a function of the collision centrality in the transverse momentum range $2 < p_\mathrm{T} < 7$ GeV/$c$ are presented. These results are also compared with the final ones previously obtained in Pb--Pb collisions at $\sqrt{s_\mathrm{NN}}$ = 2.76 TeV.

Strangeness production in Pb-Pb collisions at LHC energies with ALICE20m

The results on the production of strange and multi-strange hadrons ($K_{0}^{S}$, $\Lambda$, $\Xi$ and $\Omega$) measured with ALICE in Pb-Pb collisions at the top LHC energy of $\sqrt{s_{\rm NN}}~=~5.02~TeV$ are reported.

Thanks to its excellent tracking and particle identification capabilities, ALICE is able to measure weakly decaying particles through the topological reconstruction of the identified hadronic decay products. Results are presented as a function of centrality and include transverse momentum spectra measured at central rapidity, $p_{\rm T}$-dependent $\Lambda/K_{0}^{S}$ ratios and integrated yields. A systematic study of strangeness production is of fundamental importance for determining the thermal properties of the system created in ultrarelativistic heavy ion collisions. In order to study strangeness enhancement, the yields of studied particles are normalised to the corresponding measurement of pion production in the various centrality classes. The results are compared to measurements performed at lower energies, as well as to different systems and to predictions from statistical hadronization models.

Strange and Multi-strange Particle Production in pPb and PbPb with CMS20m

Identified particle spectra provide an important tool for understanding the particle production mechanism and the dynamical evolution of the medium created in relativistic heavy ion collisions. Studies involving strange and multi-strange hadrons, such as $K^0_S$, $\Lambda$, $\Xi^-$, and $\Omega^-$, carry additional information since there is no net strangeness content in the initial colliding system. Strangeness enhancement in AA collisions with respect to pp and pA collisions has long been considered as one of the signatures for quark-gluon plasma (QGP) formation. Recent observation of collective effects in high-multiplicity pp and pA collisions raise the question of whether QGP can also be formed in the smaller systems. Systematic studies of the strange particle abundance, particle ratios, and nuclear modification factors can shed light on this issue. The CMS experiment has excellent strange-particle reconstruction capabilities over a broad kinematic range, and dedicated high-multiplicity triggers in pp and pPb collisions. The spectra of $K^0_S$, $\Lambda$, $\Xi^-$, and $\Omega^-$ hadrons have been measured in various multiplicity and rapidity regions as a function of $p_T$ in pp, pPb, and PbPb collisions for several collision energies. The spectral shapes and particle ratios are compared in the different collision systems for events that have the same multiplicity and interpreted in the context of hydrodynamics models. Nuclear modification factors are measured out to high-$p_T$ in minimum bias pPb collisions in several rapidity regions with the goal of investigating possible modifications in hard-scattering processes using identified hadrons. Forward-backward rapidity yield asymmetries are also studied as a function of pt to search for initial state effects, such as shadowing in the nuclear parton distributions.

BBG 161

The main physics goal of the NA61/SHINE ion program is the study of the properties of the onset of deconfinement and the search for signatures of the critical point of strongly interacting matter. These goals are pursued by performing an energy and system size scan.

In this talk recent analysis results of Ar+Sc and Be+Be interactions at SPS energies are discussed. Rapidity and transverse mass spectra of pions obtained with the "h$^{-}$" analysis method are presented. The newly obtained data is compared with recently published measurements on p+p collisions.

The procedure of obtaining the final $\pi^{-}$ multiplicities is presented. The mean number of wounded nucleons $\langle W\rangle$ extracted from the EPOS MC model is used to obtain the $\langle \pi^- \rangle/\langle W\rangle$ ratio. Using data from other experiments, the comparison of $\langle \pi^{-} \rangle/\langle W\rangle$ for different measurements is discussed.

Relativistic heavy-ion collisions produce a state of matter with surprising fluid properties. The study of the vorticity allows us to access a fundamental property of this matter. The STAR experiment at RHIC has observed for the first time a significant alignment between the angular momentum of the medium produced in non-central collision and the spin of $\Lambda$($\overline{\Lambda}$) hyperons ($J$$=$1/2), revealing that the matter produced in heavy-ion collisions is by far the most vortical system ever observed. Such vorticity is expected to be maximal at the equator, and due to the low viscosity of the system, the vorticity may not propagate efficiently to the poles. This may lead to a larger in-plane than out-of-plane polarization for hyperons.
The same strong vorticity, when acting together with particle production mechanisms (e.g. coalescence and hadronization) may also influence the spin alignment of $\phi$-mesons ($J$$=$1). In this talk, we will present azimuthal angle (with respect to the reaction plane) dependence of $\Lambda$ and $\bar{\Lambda}$ polarization in $20-50\%$ central Au+Au collisions at $\sqrt{s_{NN}}$ = 200GeV. We will also present $\phi$-meson spin alignment parameters in Au+Au collisions at $\sqrt{s_{NN}}$ = 19.6, 27, 39, 62.4 and 200GeV, as a function of centrality and transverse momentum. The implications of our results on vorticity and particle production mechanisms will be discussed.

Measurements of spin alignment of vector mesons and global polarization of hyperons with ALICE at the LHC20m

Spin alignment of vector mesons (e.g. K$^{\star}$$^{0}$) and global polarization of hyperons (e.g. $\Lambda$) in non-central high energy heavy-ion collisions could occur due to large initial angular momentum of the system. The spin alignment could also occur during the process of hadronization. The spin alignment of K$^{\star}$$^{0}$ is measured using a parameter $\rho_{00}$ characterising the angular distribution of the vector mesons w.r.t. the normal to the production plane at midrapidity. The measurements of $\rho_{00}$ will be presented for pp collisions at $\sqrt{s}$ = 13 TeV and for Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 2.76 TeV. The centrality dependence of $\rho_{00}$ will also be presented. The $\rho_{00}$ values for K$^{\star}$$^{0}$ vector mesons are compared to the corresponding values for K$\mathrm{_S}^{0}$ mesons in Pb-Pb collisions. The global polarization measurements for $\Lambda$ and $\bar{\Lambda}$ hyperons will be presented for different collision centralities in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 2.76 TeV. The dependence of global polarization of hyperons on their transverse momenta and rapidity will also be presented.

Estimation of the isothermal compressibility from event-by-event multiplicity fluctuation studies20m

Fluctuations of various observables in heavy-ion collisions at ultra-relativistic energies have been extensively studied in literature as they provide important signals regarding the formation of the Quark Gluon Plasma. In addition to being sensitive to the QCD phase transitign, the multiplicity fluctuations affect other event-by-event measurements. In this work, the centrality-dependence and beam-energy dependence (from RHIC to LHC energies,i.e, from 7.7 GeV/A to 5.5TeV/A) of multiplicity fluctuations (measured by obtaining scaled variance, defined by variance scaled over mean, from the multiplicity distributions) using event generators HIJING, AMPT-Default and AMPT-String Melting will be presented and discussed. The importance of selection of proper centrality window and centrality binwidth correction will be discussed in details. The colliding system may be considered as a thermal system in Grand Canonical Ensemble (GCE) and the multiplicity fluctuations are directly proportional to the isothermal compressibility (k_{\rm T}) via the following equation :
\frac{\sigma^{\rm 2}}{\mu^{\rm 2}} = \frac{k_{\rm B}T}{V}k_{\rm T}
Therefore, it is possible to estimate the value of the isothermal compressibility ($k_{\rm T}$) at the thermal freeze-out (where the elastic processes cease to
occur and the system breaks off into smaller parts) as a
function of T and V following the above equation. The left hand side of
the equation, i.e, the multiplicity fluctuations over mean, can be measured from experiment or from event generators per centrality class at the final-state corresponding to the thermal freeze-out. For a given centrality class it can be assumed that all the events correspond to a system with the same T and V. Earlier, at chemical freeze-out, because of the expansion of the system, the temperature of
the fire ball decreases to a point where the interactions changing the number of particles are ceased. Thus, the inelastic collisions cease to occur.
Therefore, chemical composition of the system is fixed. However, the hadrons produced in the final-state in a heavy ion collision are in thermal as well as
chemical equilibrium. These quantities may be
recalculated at the higher temperature, i.e, at the
chemical freeze-out. Following this procedure, in this work, the estimation of the isothermal compressibility will be presented using the event generators AMPT, UrQMD and EPOS, for a large range of energies (from 7.7 GeV/A to 5.5TeV/A). This is a very interesting work as the isothermal compressibility has been measured first time for high energy heavy ion collision systems. Additionally, the theoretical estimation of the isothermal compressibility will be presented from Hadron Resonance Gas (HRG) model also. A comparison of the values of the isothermal compressibility with the values available for nuclear (lower) energies, water, etc, will also be presented and discussed. This study will help a lot to understand about the collision systems for a large energy range and effects of pressure on the systems. This wil also provide a baseline to study isothermal compressibility in the experiments, i.e, at RHIC and LHC energies.

BBG 165

Parallel session freeze-out

Convener:
Jean Cleymans
(Department of Physics)

14:15

Role of repulsive interactions in the interplay with missing strange resonances20m

The standard implementation of the statistical model assumes point-like particles, and accounts for attractive interactions among hadrons through resonance formation.
The classical HRG model has proven to be unable to describe all the available results on fluctuations of B/Q/S conserved charges from lattice calculations, and shows some significant deviations from the latest measurements performed by the ALICE collaboration on particles yields [1].
Motivated by these issues it has been proposed to include in the hadronic spectrum not-yet detected states from the Quark-Model [2]. The presence of extra strange resonances, which fills the gap in the poorly known strange sector, improves the description of some key-observables and at the same time spoils the agreement with other not negligible ones.
Recently the relevance of repulsive channels against some particular mesonic states, i.e. the highly debated sigma and kappa resonances, has been highlighted [3,4], and furthermore it has been shown how repulsive interactions are important to have a consistent description of SU2 and SU3 gauge theories [5].
Repulsive interactions can be modeled within the HRG framework assigning to each particle an effective hard-sphere radius, with the net result that the portion of space occupied by hadrons must be subtracted to the system-volume [6], namely excluded-volume effects.
Although this is a simplicistic assumption, it allows to extract quantitative results on the different hadronic interaction-channels, e.g. the so called proton-anomaly can be interpreted as a difference in the light and strange sectors [7].
We show how the inclusion of repulsive interactions balances the effect of extra higher-mass strange resonances restoring the agreement with higher-order fluctuations of conserved charges, and preserving the improvements for the above mentioned key observables and for experimental particle yields.
Indeed both theoretical calculations and experimental measurements hint consistently for smaller strange states with respect to the light ones with same mass. This result can be phenomenologically justified by the smaller cross sections for the heavier strange hadrons.
Future calculations on higher-order observables related to net-electric charge could further establish the role of repulsive interactions.
Excluded-volume effects could be otherwise relevant to analyze the non-monotonic behavior of the Beam Energy Scan measurements on fluctuations of conserved charges at non-vanishing baryon densities.

The conventional approach to treat strangeness freezeout has been to consider a unified freezeout scheme where strangeness freezes out along with the non-strange hadrons (1CFO), with or without an additional parameter accounting for out of equilibrium
strangeness production ($\gamma_S$). Several alternate scenarios have been formulated lately- i. to consider a hadronic afterburner post hadronisation that allows for a microscopic and dynamic description of freezeout, ii. to consider out of equilibrium production of strange as well as non-strange hadrons, iii. to introduce flavor dependent hadron mass - eigenvolume relationship within a Van der Waal's excluded volume approach, and iv. allowing for early freezeout of strangeness within a complete thermal and chemical
equilibrium approach (2CFO).
In this talk, we will focus on this last approach, 2CFO in comparison to 1CFO and its variants with respect to the roles played by the system size and missing resonances predicted by different theoretical approaches but yet to be seen in experiments.
We have compared the performance of different freezeout scenarios like 1CFO, 1CFO$+\gamma_S$ and 2CFO across all available centralities for Pb+Pb, p+Pb and p+p at $\sqrt{s_{NN}}=$ 2.76, 5.02 and 7 TeV respectively- in doing so we are able to analyse the freezeout properties over three orders of magnitude in terms of the mid-rapidity charged multiplicity as well as the extracted freezeout volume parameter. We find that the performance of 1CFO with/without $\gamma_S$ is insensitive to system size. However, 2CFO exhibits a clear system size dependence- while for Pb+Pb the $\chi^2/NDF$ is around 0-2, for smaller system size in p+Pb
and p+p, the $\chi^2/NDF>5$. This clearly shows a system size dependence of the preference for the freezeout scheme- while 2CFO is preferred in Pb+Pb, 1CFO$+\gamma_S$ is preferred in
p+Pb and p+p. We have further investigated the role of the missing resonances on strangeness freezeout across SPS to LHC beam energies. We study several decay schemes for these missing resonances and estimate their influence on the strange chemical potential, performance of the different freezeout schemes as well as on the choice of the extracted freezeout parameters.

Speaker:
Sandeep Chatterjee
(AGH University of Science and Technology, Krakow)

We present results from the Rope Hadronization model, implemented in the DIPSY Monte Carlo event generator, specifically regarding production of strangeness in small systems. The Rope Hadronization model is built on the Lund String Hadronization model. It allows for interactions between strings in dense environments. The interacting strings form "colour ropes", characterized by their SU(3) multiplet structure. From lattice calculations we know that ropes have an increased string tension compared to normal strings. This gives rise to increased strange/non-strange hadron yield ratios, as well as flow-like effects. The inclusion of Rope Hadronization greatly improves the description of data from RHIC and LHC.

Baryon spectra and antiparticle/particle ratios from the improved AMPT model20m

The string melting version of a multi-phase transport model is often applied to high energy heavy ion collisions since the formed dense matter is expected to be in parton degrees of freedom. In this work we improve its quark coalescence component, which describes the hadronization of the partonic matter to a hadronic matter. We have removed the previous constraint that forced the numbers of mesons, baryons, and antibaryons in an event to be separately conserved through the quark coalescence process. A quark now could form either a meson or a baryon depending on the distance to its coalescence partner(s). We then compare results from the improved model with the experimental data on hadron dN/dy, $p_{T}$ spectra, and $v_{2}$ in heavy ion collisions from $\sqrt{s_{NN}}$ = 62.4 GeV to 5.02 TeV. We show that, besides being able to describe these observables for low-$p_{T}$ pions and kaons, the improved model also better describes the low-$p_{T}$ baryon observables in general,especially the baryon $p_{T}$ spectra and antibaryon-to-baryon ratios for multi-strange baryons.

COSMOS

Koningsberger

Production cross-sections and nuclear modification factor for charmed baryons and mesons in p-Pb collisions at 5 TeV with the LHCb detector20m

The study of the nuclear modification factor and the forward/backward
asymmetry in p-Pb collisions at $\sqrt(s_{NN})$=5 TeV is extended to
the $\Lambda_c$ baryon, providing the first measurement of charmed
baryon production in pA collisions. The result is compared to the
analogous measurement on charmed mesons, providing an insight on the
production mechanism of charmed hadrons.

Low mass dielectrons in pp at 13 TeV, p-Pb at 5.02 TeV and Pb-Pb collisions at 2.76 TeV measured by the ALICE experiment20m

Dielectrons produced in ultra-relativistic heavy-ion collisions at the LHC provide a unique probe of the whole system evolution as they are unperturbed by final-state interactions. The dielectron continuum is extremely rich in physics sources: on top of ordinary Dalitz and resonance decays of pseudoscalar and vector mesons, thermal black-body radiation is of particular interest as it carries information about the temperature of the hot and dense system created in such collisions. Dielectron invariant-mass distribution is furthermore sensitive to medium modifications of the spectral function of short-lived vector mesons that are linked to the potential restoration of chiral symmetry at high temperatures. Correlated electron pairs from semi-leptonic charm and beauty decays provide complementary information about the heavy-quark energy loss.

In this talk, we will present an extensive summary of the LHC Run-1 results from the ALICE experiment in all three collisions systems: pp, p-Pb and Pb-Pb, the former two providing crucial vacuum and cold-nuclear matter references for the latter. Furthermore, we will discuss the latest results of the analysis of Run-2 pp collisions at 13 TeV collected with a trigger on high charged-particle multiplicities and report on the progress made employing multivariate analysis techniques being developed by ALICE.

Charmed meson and baryon measurements in pp and p-Pb collisions with ALICE at the LHC20m

Charm production in proton-proton collisions can be described by perturbative QCD calculations down to low transverse momentum ($p_\mathrm{T} \sim 0$), due to the large mass of the charm quark ($m_c >> \Lambda_{QCD}$). The measurement of charm production is thus important to constrain theoretical predictions. In p-Pb collisions, the study of charm production can help disentangle cold nuclear matter effects from the modification of the $p_\mathrm{T}$ spectrum of charm in Pb-Pb collisions due to the high-temperature and high energy-density medium formed.

Hadronisation is a non-perturbative process, and as such experimental input is crucial to guide theoretical models. The charmed baryon-to-meson ratio ($\mathrm{\Lambda_{c}^+} / \mathrm{D^0}$) is sensitive to hadronisation mechanisms in pp and p-Pb collisions. Furthermore the measurement of heavier charmed baryons such as $\mathrm{\Xi_c^0}$ will help to quantify the hadronisation of c quarks to different hadron species. Measurements of charmed baryon production in pp and p-Pb collisions also provide a baseline for future measurements of charmed baryons in Pb-Pb collisions, where the baryon-to-meson ratios will offer a unique probe of thermalisation and hadronisation mechanisms, in particular constraining the role of coalescence and predicted presence of diquark states in the medium.

We present here recent open heavy-flavour results in pp and p-Pb collisions from the ALICE experiment. These include measurements of the D-meson production cross sections, nuclear modification factor in p-Pb collisions, and studies as a function of multiplicity. We also present new results from the ALICE experiment of the $p_\mathrm{T}$-differential cross section of the $\Lambda_{c}^+$ baryon in pp collisions, and in p-Pb collisions - the first heavy-ion measurement of a charmed baryon at the LHC. In addition, the $p_\mathrm{T}$-differential cross section times branching ratio of the $\mathrm{\Xi_c^0}$ baryon measured in the decay channel $\mathrm{\Xi_c^0 \to e\Xi^-\nu_e}$ in pp collisions will be presented - the first measurement of $\mathrm{\Xi_c^0}$ baryon production at the LHC.

Quarkonium production in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV with ALICE20m

The ultra-relativistic heavy-ion collisions at the Large Hadron Collider provide an unique opportunity to study the properties of matter at extreme energy densities where a phase transition of the hadronic matter to a deconfined medium of quarks and gluons, the Quark-Gluon Plasma (QGP) is predicted. Considerable theoretical and experimental efforts have been invested in the last 30 years to study the properties of the QGP.

Among the prominent probes of the QGP, heavy quarks play a crucial role since they are created during the initial stages of the collision, before the QGP formation, and their number is conserved throughout the partonic and hadronic phases of the collision. The sequential suppression of the quarkonium states was suggested as a signature of the QGP. Later, a regeneration of quarkonia by recombination of deconfined quarks was also predicted. The first results on quarkonium suppression in Pb-Pb collisions at the LHC seem to indicate that for charmonia both regeneration and supression mechanisms play a role, while for bottomonia the regeneration mechanism should be small.

The momentum space azimuthal anisotropy of charmonium production, quantified using the second harmonic Fourier coefficient (referred as elliptic flow), provides important information on the magnitude and dynamics of charmonium suppression and regeneration mechanisms, both of them thought to be at their highest level at LHC energies.

ALICE measures quarkonia at mid-rapidity in the dielectron decay channel and at forward rapidity in the dimuon one, both down to zero transverse momentum. Single- and multi-differential measurements of quarkonium nuclear modification factor at forward rapidity and J/$\psi$ elliptic flow in Pb-Pb collisions (both at forward and mid-rapidity) at $\sqrt{s_{NN}} = 5.02$ TeV as a function of centrality, transverse momentum and rapidity will be presented, with largely increased statistics compared to $\sqrt{s_{NN}} = 2.76$ TeV. Comparisons to measurements at different collision energies and available theoretical calculations will be discussed.

BBG 169

Parallel session strangeness in astrophysics

Convener:
David Blaschke
(University of Wroclaw)

14:15

SU(3) PNJL model with thermomagnetic couplings and compact stars20m

In a recent letter, Physics Letters B 767 (2017) 247–252, we presented a an SU(2) NJL model with a coupling wich depends on the magnetic field in order to calculate the neutral pion mass at T = 0. In this work, we improve our model by adding the strange quark, the Polyakov loop and finite temperature. We then build a thermomagnetic dependence for the G and K couplings of the SU(3) PNJL model by fitting lattice QCD calculations for the average and the difference of u and d quark condensates under a strong magnetic field. With the new couplings, we compute several thermodynamic quantities and generate an equation of state for magnetized quark matter which we use to determine the mass-radius relation for compact stars from the integration of the TOV equations.

Towards a unified quark-hadron equation of state for neutron stars, supernovae and heavy-ion collisions20m

The aim of our work is to develop a unified equation of state (EoS) for nuclear and quark matter for a wide range in temperature, density and isospin so that it becomes applicable for heavy-ion collisions as well as for the astrophysics of neutron stars, their mergers and supernova explosions. As a first step, we use improved EoS for the hadronic and quark matter phases and join them via Maxwell construction.
For this we work with a generalized density functional approach for the self energies in a quasi particle picture, which gives us the possibility to start with a reasonable physical basis and apply improvements to fit certain constraints from lattice QCD and neutron star measurements.

Recently the CERN ALICE experiment, in its dedicated cosmic ray run, observed muon bundles of very high multiplicities, thereby confirming similar findings from the LEP era at CERN (in the CosmoLEP project). Originally it was argued that they apparently stem from the primary cosmic rays with a heavy masses.

We propose an alternative possibility arguing that muonic bundles of highest multiplicity are produced by strangelets, hypothetical stable lumps of strange quark matter infiltrating our Universe. We also address the possibility of additionally deducing their directionality which could be of astrophysical interest. Significant evidence for anisotropy of arrival directions
of the observed high multiplicity muonic bundles is found. Estimated directionality suggests their possible extragalactic provenance.

Gravitational waves from binary compact star mergers in the context of strange matter20m

One hundred years after Albert Einstein developed the field equations of general relativity and predicted the existence of gravitational waves (GWs), these curious spacetime-ripples have been observed from a pair of merging black holes by the LIGO detectors. As GWs emitted from merging neutron star binaries are on the verge of their first detection, it is important to understand the main characteristics of the underlying merging system in order to predict the expected GW signal. Based on a large number of numerical-relativity simulations of merging neutron star binaries, the emitted GW and the interior structure of the generated hypermassive neutron stars (HMNS) have been analyzed in detail. This talk will focus on the internal and rotational HMNS properties and their connection with the emitted GW signal. Especially, the appearance of the hadon-quark phase transition and the formation of strange matter in the interior region of the HMNS and its conjunction with the spectral properties of the emitted GW will be addressed. arXiv:1611.07152

Coffee corner, Koningsberger building

16:05
→
17:45

Parallel Freeze-out: 2BBG 165 ()

BBG 165

Parallel session freeze-out

Convener:
Pengfei Zhuang
(Tsinghua University)

16:05

Baryons in the plasma: in-medium effects and parity doubling20m

We investigate the fate of the light baryons in the hadronic and the quark-gluon plasma. In the confined phase a strong temperature dependence is seen in the masses of the negative-parity groundstates, while at high temperature parity doubling emerges. We study baryons with different strangeness and find a noticeable effect of the heavier s quark. This study uses nonperturbative lattice simulations, employing the FASTSUM anisotropic Nf=2+1 ensembles.

Extension of the ideal hadron resonance gas (HRG) model is constructed which includes attractive and repulsive van der Waals (VDW) interactions between hadrons [1]. The model employs a novel multi-component quantum statistical VDW approach which incorporates the Fermi-Dirac and Bose-Einstein effects in the system of interacting particles.
The VDW parameters a and b are fixed by the ground state properties of nuclear matter, and this VDW-HRG model yields the nuclear liquid-gas transition at low temperatures and high baryonic densities.

The predictions of the model are confronted with the lattice QCD calculations at zero chemical potential.
The inclusion of VDW interactions between baryons leads to a qualitatively different behavior of cumulants of fluctuations of conserved charges, for many observables closely resembling the lattice QCD results.
We also explore the effect of VDW interactions on the thermal fits to heavy-ion hadron yield data and find that existing agreement of ideal HRG is not spoiled in the VDW-HRG model.
The VDW interactions are found to have a substantial influence on the higher orders of fluctuations of conserved charges at finite chemical potential, in the regions where chemical freeze-out in heavy-ion collisions is expected to occur. Thus, the nuclear liquid-gas transition manifests itself into non-trivial net-baryon fluctuations in heavy-ion collisions.

Finally, we explore the lattice QCD observables at imaginary chemical potential and also phase shifts of nucleon-nucleon scattering. Both are found to be consistent with a presence of significant repulsive interactions between baryons.

We present several results on the temperature dependence of hadronization and hadron freeze out by using different approaches. We apply the Polyakov-Nambu-Jona-Lasinio model to generate the low-lying mesons and baryons with strangeness at finite temperature. We find a flavor-dependent pattern in the temperature of the effective deconfinement, similarly to what is found in recent lattice calculations for the QCD phase transition, favouring a hotter transition for states with strangeness. In addition, we use a simple model of a medium in a Friedmann-Robertson-Walker spacetime, which mimics the expansion of a fireball in a heavy-ion collision. This model presents a well-defined decoupling mechanism, whose temperature can be easily extracted versus the mass and the cross section of the particles in the bath. Our findings support a sequential freeze out in relativistic heavy-ion collisions.

Mass hierarchy and energy scaling of the Tsallis--Pareto parameters in hadron productions at RHIC and LHC energies20m

The identified hadron spectra measured in high energy particle collisions are one of the most fundamental observable quantities. They accumulate information about all the processes during the collisions. They may carry information about all the microscopical and collective processes which occur during high-energy collisions, therefore it is essential to measure and analyze them as precise as possible in a wide energy range. We need to analyze not just the experimental data but also the result of theoretical and Monte Carlo event generators, that contain all of the latest physical phenomena and effects. This can give us feedback for future models of the hadron formation.

Using the latest, high-accuracy experimental data we could investigate the energy dependence of the Tsallis--Pareto fit parameters, indeed observing mass and c.m. energy scaling of the hadron production in proton-proton collisions [1,2].
Using the q-entropy formula, we may interpret the microscopic physics in terms of the Tsallis $q$ and $T$ parameters. This gives us another excellent opportunity to compare the parameters of baryons with those of mesons or even strange particles with the non-strange ones.

In this presentation we extend our above study and investigate the mass hierarchy and the energy effect of the strange and heavy hadronic states and also compare our result to the results of the HIJING++, our soon-to-be published Heavy Ion Jet Interaction Generator [3].

Production of (anti-)(hyper-)nuclei production at LHC energies with ALICE20m

The ALICE experiment has measured a variety of (anti-)(hyper-) nuclei produced in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV and at 2.76 TeV. In addition, a large sample of high quality data was recorded in pp collisions at $\sqrt{s} = 7$ TeV and 13 TeV and in p-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5 TeV. These data are used to study the production of a variety of (anti-)(hyper-)nuclei produced in the collisions, namely (anti-)deuteron, (anti-)helium-3, (anti-)alpha and (anti-)hypertriton. The identification of these (anti-)(hyper-)nuclei is based on the energy loss measurement in the Time Projection Chamber and the velocity measurement in the Time-Of-Flight detector. In addition, the Inner Tracking System is used to distinguish secondary vertices originating from weak decays from the primary vertex. New results on deuteron production as a function of multiplicity in pp, p-Pb and Pb-Pb collisions will be presented, as well as the measurement of helium-3 in p-Pb and Pb-Pb collisions. Special emphasis will be put on new results of the hypertriton in its 2- and 3-body decay modes. Additionally, the high energy deposit of Z=2 particles in the Transition Radiation Detector has been exploited to collect a hardware-triggered data sample in the high-interaction rate p-Pb collisions at $\sqrt{s_{\rm NN}}$ = 8.16 TeV. First findings from this (anti-)nuclei enriched sample will be shown. The large variety of measurements at different energies and system sizes allows to constrain the models of the production mechanisms of light flavour baryon clusters, in particular those based on coalescence and the statistical hadronisation approaches.

COSMOS

Koningsberger

We describe the propagation of heavy quarks in the quark-gluon plasma (QGP) by means of
a Boltzmann transport approach. We take into account the non-perturbative interaction between
heavy quarks and light quarks by means of a quasi particle approach in which light partons are
dressed with thermal masses. Such a model is able to catch the main features of non-perturbative
interaction as the increasing of the interaction in the region of low temperature, which is a fundamental ingredient to reproduce the experimental data for the nuclear suppression factor and the
elliptic flow. A main finding is that one predicts both $R_{AA}$ and $v_2$ with an underlying space-diffusion coefficient that ,within
the present uncertainties is in good agreement with present lQCD calculations.
We will also highlight the impact of radiative energy loss contribution implementing in our model
a formula for the emitted gluon spectrum calculated in a multiple scattering and higher-twist scheme.
Besides it turns out that charm quarks may be an ideal probe of the initial electromagnetic field.
In fact thanks to their short formation time, subdominant thermal production and not very
large mass they can be a sensitive probe of the initial electromagnetic field and electric conductivity of the bulk matter.
Realistic simulation shows a charm/anti-charm opposite transverse flow $v_1$ of the order of a few
percent depending on the value of the electric conductivity
of the bulk QGP.

Quarkonium measurements in heavy-ion collisions with the STAR experiment20m

Measurements of quarkonium production have played an important role in understanding the properties of the Quark-Gluon Plasma (QGP) formed in relativistic heavy-ion collisions. Quarkonium suppression in the medium due to the color screening effect has been proposed as a direct signature of the QGP formation. However, other effects, such as cold nuclear matter (CNM) effects and regeneration, add additional complications to the interpretation of the observed suppression. Measurements of $J/\psi$ suppression and elliptic flow ($v_{2}$) over a broad kinematic range in different collision systems can help disentangle the various mechanisms contributing to the observed $J/\psi$ modification. Compared to charmonia, bottomonia receive less regeneration contribution due to the smaller bottom quark cross-section, thus providing a cleaner probe. Furthermore, different bottomonium states of different binding energies are expected to dissociate at different temperatures, and measurement of this "sequential melting" can help constrain the medium temperature.
In this talk, we will present the latest measurements of $J/\psi$ and $\Upsilon$ productions in p+p, p+Au and Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV and in U+U collisions at $\sqrt{s_{NN}}$ = 193 GeV by the STAR experiment. Based on the data taken in year 2015, the $J/\psi$ and $\Upsilon$ measurements in p+p collisions provide new baselines for A+A collisions, while the measurements in p+Au collisions can help quantify the CNM effects. The double ratio of $\psi$(2S) to $J/\psi$ production rates between p+p and p+Au collisions is measured at mid-rapidity for the first time. The nuclear modification factor ($R_{\rm{AA}}$) and $v_{2}$ as a function of transverse momentum $p_{\rm{T}}$ for $J/\psi$ in both Au+Au and U+U collisions will be shown to distinguish different effects. Furthermore, the $R_{\rm{AA}}$ for different $\Upsilon$ states will be presented as a function of $p_{\rm{T}}$ and centrality, and compared to that measured at the LHC as well as theoretical calculations.

Recent ALICE collaboration measurements[1] showed a significant excess in J/$\psi$ yield at very low transverse momenta ($p_{T}<0.3$ GeV/$c$) in the peripheral Pb+Pb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV. The same behavior of the J/$\psi$ production is observed at STAR in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV. These results are interpreted as coherent photoproduction of J/$\psi$ at the moment. The coherent photoproduction scenario may also suggest there is an excess of photoproduced electron-positron production at the very low $p_{T}$ in peripheral collisions. It would be very interesting to investigate the electron-positron pair production in the full mass region ($M_{ee}<4 $GeV/$c^{2}$) at very low $p_{T}$ in heavy-ion collisions in different centrality bins. If the coherent photoproduction mechanism is confirmed, the coherently photoproduced $e^{+}e^{-}$ pairs accompanying violent hadronic collisions may provide a novel probe of the hot and dense nuclear matter.

In this talk, we will present $e^{+}e^{-}$ invariant mass spectra in very low $p_{T}$ in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV and U+U collisions at $\sqrt{s_{NN}}$ = 193 GeV. The $p_{T}$ spectra from different mass regions (0.4-0.76, 1.2-2.6, and 2.8-3.2 GeV/$c^{2}$) will be reported. The structure of t (-t = $p_{T}^{2}$ ) distributions of these mass regions and comparisons with that in ultra-peripheral collisions will be shown. The centrality dependence of the $e^{+}e^{-}$ productions will be shown. Physics messages will be discussed.
\vspace{3mm}

Heavy quarks are useful probes to investigate the property of the hot and dense medium
created in high energy heavy ion collisions because they are produced via initial hard scattering
and thus are affected by the entire evolution of the medium.
The PHENIX experiment has measured open heavy flavor production via the measurement of
single lepton from the decay of inclusive heavy quarks in various collision systems.
After the addition of the barrel and forward silicon vertex tracker (VTX and FVTX),
we are able to measure the bottom and charm production separately using the off-vertex decays.
In addition, non-prompt $J/\psi$ from $B$ decay is a clean channel to measure the open bottom production.
In this talk, we will present the nuclear modification of single electrons from
bottom and charm decays separately in Au+Au collisions at mid-rapidity and
non-prompt $J/\psi$ in Cu+Au collisions at forward rapidity, and discuss their interpretations.

Centrality and transverse momentum dependence of $J/\psi$ production in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$=5.02 TeV at mid-rapidity with ALICE20m

ALICE at the Large Hadron Collider (LHC) provides unique capabilities to study charmonium production at low transverse momenta. In the early and hottest phase of nucleus-nucleus collisions the formation of a Quark-Gluon Plasma (QGP) is expected. Several QGP induced effects, such as the suppression of charmonium states due to color screening and/or an enhancement due to (re)combination of uncorrelated charm and anti-charm quarks, can play a role. While a suppression of $J/\psi$ with respect to binary-scaled pp collisions was indeed observed in heavy-ion collisions at lower energies, recent measurements in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$=2.76 TeV indicate that (re)combination seems to dominate the $J/\psi$ yield in the low $p_{\rm T}$ region at LHC energies.

At central rapidity, corresponding to the range $|y|<0.9$, $J/\psi$ are reconstructed down to zero $p_{\rm T}$ via their decay into two electrons. This kinematic selection also enables the measurement of coherent $J/\psi$ photo-production at very low transverse momentum, similar to the measurements done in ultra-peripheral collisions, where the nuclei interact only electromagnetically.

In this talk we will present new results on the inclusive $J/\psi$ nuclear modification factor $R_{\rm AA}$ as a function of centrality and transverse momentum in Pb-Pb collisions at $\sqrt{s_{NN}}$=5.02 TeV. In addition we will present the centrality dependent $J/\psi$ photo-production cross-section. The $p_{\rm T}$ distribution shape and the $p_{\rm T}$-integrated yields in the typical region for coherent production will be shown and compared to model
expectations.

BBG 161

Parallel session resonances

Convener:
Frank Geurts
(Rice University (US))

16:05

First Measurement of the energy dependent N* production amplitude with a Partial Wave Analysis20m

The production of hadrons with strange quarks within nuclear matter is fundamental to unravel the mystery about the content of neutron stars. A large fraction of strange hadrons are produced by resonances with broad masses that can undergo interference effects before they decay into strange hadrons.
We present here the first determination of the production amplitude of N*->p+Kaon+Lambda for resonances with masses between 1650 and 1900 MeV/c^2 and an excess energy up to 700 MeV via a partial wave analysis. The resonance amplitudes were extracted by analysing the reaction p+p -> pKLambda measured in seven different data samples for fixed target experiments at kinetic energies between 1.9 and 4.3 GeV by the COSY-TOF, DISTO, FOPI and HADES collaborations. This work establishes a new paradigm in the understanding of strange hadrons production and opens up the precision era for the investigation of strangeness production in nucleon nucleon reactions.

Reduction of the K* meson abundance and kinetic freeze-out in heavy ion collisions20m

We discuss the relation between the reduction of the K* meson abundance and the kinetic freeze-out in heavy ion collisions. We evaluate the absorption cross sections of the K* meson by light mesons during the hadronic stage, and investigate effects on the K* meson abundance from both the hadronic interactions and decay of K* mesons. We show how the interplay between the interaction of the K* meson and kaon with light mesons in the hadronic medium determines the final yield difference of the statistical hadronization model to the experimental measurements. We also argue that the larger suppression of the yield ratio, K*/K at LHC than at RHIC compared to the expectations from the statistical hadronization model is related to different kinetic freeze-out conditions at RHIC and LHC.

Probing the hadronic phase with resonances of different lifetimes in ALICE at the LHC20m

The ALICE experiment has measured the production of a rich set of hadronic resonances, such as $\rho^0(770)$, K$*^0(892)$, $\phi(1020)$, $\Sigma^\pm(1385)$, $\Lambda(1520)$ and $\Xi^0(1530)$, in pp, p-Pb and Pb-Pb collisions at various energies at the LHC. A comprehensive overview and the latest results will be presented in this talk. Transverse momentum spectra, mean transverse momenta and particle production ratios will be discussed as a function of multiplicity/centrality and collision energy. Results are compared to Monte Carlo event generators, including EPOS3 with UrQMD afterburner, and predictions from statistical hadronisation models. Special focus will be given to the role of hadronic resonances for the study of final-state effects in high-energy collisions. In particular, the measurement of resonance production in heavy-ion collisions has the capability to provide insight into the existence of a prolonged hadronic phase after hadronisation. If such hadronic phase lasts long enough, the decay daughters of very shortlived resonances experience its full evolution and suffer re-scattering in the dense hadronic medium, which could modify their correlations and hence the experimentally measured resonance yields. The observation of the suppression of the production of $\Lambda(1520)$ resonances in central Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 2.76$ TeV adds further support to the existence of such a dense hadronic phase, as already evidenced by K*/K and $\rho/\pi$ measurements.

A chemical non-equilibrium model with a single freeze-out appeared to be rather successful in describing the LHC ALICE data at 2.76 TeV for various particles [1,2]. The pT spectra of pions, kaons, protons, $K^*(892)^0$ and the $\phi(1020)$ are described by the same hubble-like freeze-out hyper-surface that has only one parameter for the slope of the spectra – the ratio of the freeze-out time to the freeze-out radius [1,2]. This is very surprising for the $K^*(892)^0$ and the $\phi(1020)$, because the first one is short leaving, while the second one is long living. The description of both of them may question the necessity of the long re-scattering phase, which is also successfully used to describe the ALICE data [3]. It may also indicate that the non-equilibrium, as implemented in [1,2], may effectively include the re-scattering in the non-equilibrium chemical potentials. It is important to differentiate between the equilibrium with the re-scattering, and the single sudden freeze-out in the non-equilibrium, because the non-equilibrium also leads to pion condensation [4].

A good test for the non-equilibrium single freeze-out scenario [1,2] is the comparison to different resonances, especially strange resonances, because this scenario requires a special relation between the strange and the non-strange chemical potentials, depending on the quark content of a resonance. The heavy $\Lambda$ $\Xi$ and $\Omega$ can be still described by the non-equilibrium very well, if one assumes a smaller slope for them [2]. This introduces the dependence on the mass of the resonance, but is also supported by smaller flow of heavy particles in other approaches, see e.g. [4].

In this work, the predictions for the mean multiplicities and the pT spectra of various strange resonances are made, including the $\rho(770)$, $\Lambda(1520)$, $\Xi(1530)$ and $\Sigma(1385)$.

BBG 169

Parallel session upgrades

Convener:
Joachim Stroth
(Johann-Wolfgang-Goethe Univ. (DE))

16:05

The Silicon Tracking System of the CBM experiment at FAIR20m

The Silicon Tracking System is the central detector in the CBM experiment at FAIR. Operating in the 1 Tm dipole magnetic field, the STS will enable pile-up free detection and momentum measurement of the charged-particles originating from beam-target nuclear interactions at rates between 100 kHz and 10 MHz. It will also allow identifying particle decays occurring within the aperture, in particular those with strangeness content.
The STS consists of 8 tracking stations based on double-sided silicon microstrip sensors equipped with fast, self-triggering read-out electronics. With about two million read-out channels, the STS will deliver a high-rate stream of time-stamped data that is transferred to a computing farm for on-line event determination and analysis. The functional building block is a detector module consisting of a sensor, microcables and two front-end electronics boards. The double-sided microstrip sensors have a strip pitch of 58 $\mu$m, are AC-coupled and oriented under 7.5 degree stereo angle. Double metallization is employed for read-out routing. Ultra-thin microcables with up to 60 cm length and a line pitch matching that of the sensor strips transfer the analog signals to the readout electronics at the periphery of the stations where cooling and further infrastructure can be provided without compromising the material budget. The custom-developed read-out ASIC “STS-XYTER” has a self-triggering architecture that delivers time and amplitude information. The detector will be operating within a thermal enclosure of about 2 m$^3$ at about −5 $^\circ$C so that the silicon sensors remain operational up to a particle fluence of 10$^{14}$ 1-MeV n$_{eq}$cm$^{-2}$. The electronics, 16 thousand ASICs, data aggregation and power boards, will dissipate about 40 kW that will be removed with bi-phase CO$_2$ evaporative cooling.
In this contribution, the development status of the STS components and the system integration will be discussed and an outlook on the detector construction given.

ALICE is the experiment specifically designed for the study of the Quark-Gluon Plasma in heavy-ion collisions at the CERN LHC. The ALICE detector will be upgraded during the LHC Long Shutdown 2, planned for 2019-2020, in order to fully exploit the large integrated luminosity that will be provided by the LHC in Run~3 and Run~4.

The Muon Forward Tracker (MFT), an internal tracker added in the acceptance of the existing Muon Spectrometer and designed to cover the pseudorapidity range $2.5 < \eta < 3.6$, will be part of the ALICE detector upgrade programme, allowing for a crucial improvement of the measurements presently done with the Muon Spectrometer, and giving access to new measurements. The precise measurement of the offset to the primary vertex for the muon tracks, in particular, will permit for the first time in ALICE the statistical separation of open charm ($c\tau \sim 120-300~\mu$m) and beauty ($c\tau \sim 500~\mu$m) production at forward rapidity, rejecting at the same time a large fraction of background muons coming from pion and kaon decays.

The setup of the MFT is an assembly of circular planes made of Monolithic Active Pixel Sensors (MAPS), to be installed between the interaction point and the hadron absorber of the Muon Spectrometer. The total material budget of the MFT tracking planes, the radiation hardness of their components, coupled with the high granularity of the pixel sensors and the envisaged readout speed, fulfil the conditions for the operation at the energies and luminosities foreseen for the LHC Run 3 heavy-ion programme. The ambitious programme of high-precision measurements expected to characterise the ALICE muon physics after 2020, will also impose the upgrade of the front-end and readout electronics of the existing Muon Spectrometer. A selection of results from the physics performance studies will be presented, together with an overview of the technical aspects of the upgrade project.

J-PARC is currently an accelerator complex utilizing high-intensity proton beam.
However, recently as a very attractive project, acceleration of heavy ions with
supplementing ion sources at J-PARC (called J-PARC-HI) is seriously contemplated by domestic as well as international communities.

The planned facility will accelerate up to $U^{92+}$ with beam energy 20 AGeV, which corresponds to $\sqrt{s_{NN}}$ = 6.2 AGeV.
The highlight of the J-PARC-HI is its highest beam rate up to $~10^{11}$ Hz, which will enable us to probe very rare events.
Taking advantage of this high intensity, J-PARC-HI will aggressively study new and rare observables in this energy region:

(i) nuclear medium modification of chiral property of vector mesons through low-mass di-lepton signal,
(ii) QCD critical point characterization through event-by-event fluctuation signals of particle production,
(iii)systematic measurements for equation of state through collective flow signal or two-particle momentum correlation signal, or
(iv) searching for hyper nuclei with multi strangeness including which equal or more than 3.

For such measurements, a multi purpose large acceptance spectrometer is designed, with alternative choices of a dedicated di-muon spectrometer and/or of a closed geometry spectrometer for the hyper-nucleus study.
The plan for the heavy ion at J-PARC, is aiming for the first experimental measurements in 2025. In this presentation, the global ideas for the J-PARC-HI project will be introduced.

The ALICE Collaboration is preparing a major upgrade of the ALICE detector,
planned for installation in the second long LHC shutdown. The construction is
expected to be completed by 2020 for data taking until 2029. A key element of
the ALICE upgrade is the construction of a new, ultra-light, high-resolution
Inner Tracking System (ITS).

With respect to the current ITS, this upgrade is aiming at a better position
resolution (5 micron), a lower material budget (0.3% X0) and a faster readout
(up to 100 kHz in Pb-Pb collisions). This will be obtained by seven concentric
detector layers based on an advanced Monolithic Active Pixel Sensor (MAPS)
chip, with a pixel pitch of 30x30um^2. The general layout and main components
of the new ITS, a summary of the R&D activities, the current status and an
outlook will be presented.